Court Opinion

ID: 805370
Source: CourtListenerOpinion
Date Created: 2012-07-27 14:03:54+00
Date Added: 2024-06-11T18:00:14.662560
License: Public Domain

In the

United States Court of Appeals
               For the Seventh Circuit

No. 11-3313

L EONARD L APSLEY, et al.,
                                               Plaintiffs-Appellees,
                                 v.

X TEK, INC.,
                                             Defendant-Appellant.

             Appeal from the United States District Court
       for the Northern District of Indiana, Hammond Division.
          No. 05-CV-00174—Joseph S. Van Bokkelen, Judge.

        A RGUED M AY 23, 2012—D ECIDED JULY 27, 2012

  Before M ANION, R OVNER, and H AMILTON, Circuit Judges.
  H AMILTON, Circuit Judge. This appeal arose from an
accident at a steel rolling mill that permanently
disabled one of the workers there. The circumstances of
that accident were unusual. Industrial grease was pro-
pelled in a jet with enough energy to penetrate and pass
through the human body like a bullet. That jet hit and
disabled plaintiff Leonard Lapsley. At trial the jury
found that the accident was caused by a design defect in
2                                                No. 11-3313

a heavy industrial product designed and manufactured
by defendant Xtek, and sold and installed in the mill.
That equipment contained an internal spring that could
exert over ten thousand pounds of force. The jury
accepted the theory of plaintiffs’ expert witness,
Dr. Gary Hutter, that the spring was the culprit mecha-
nism behind the accident and that an alternative design
of a thrust plate in the equipment would have prevented
the disabling accident. Xtek has appealed, challenging
the district court’s denial of its Daubert motion that
sought to bar Dr. Hutter from offering his expert
opinions, which were essential to the plaintiffs’ case.
  The purpose of the Daubert inquiry is to scrutinize
proposed expert witness testimony to determine if it
has “the same level of intellectual rigor that charac-
terizes the practice of an expert in the relevant field” so as
to be deemed reliable enough to present to a jury.
Kumho Tire Co. v. Carmichael, 526 U.S. 137, 152 (1999). A
Daubert inquiry is not designed to have the district judge
take the place of the jury to decide ultimate issues of
credibility and accuracy. If the proposed expert testimony
meets the Daubert threshold of relevance and reliability,
the accuracy of the actual evidence is to be tested
before the jury with the familiar tools of “vigorous
cross-examination, presentation of contrary evidence,
and careful instruction on the burden of proof.” Daubert
v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 596
(1993). Once the district court has adequately applied
the Daubert framework, our review of the determination
to admit or exclude the evidence is deferential. E.g.,
United States v. Lupton, 620 F.3d 790, 798-99 (7th Cir. 2010)
No. 11-3313                                              3

(affirming exclusion of expert testimony); see also
Kumho Tire, 526 U.S. at 152 (reversing court of appeals
decision that failed to accord sufficient discretion to
district court that admitted expert testimony). In this
case, the district court’s stated analysis of the proposed
testimony was brief, but it was also directly to the
point and was sufficient to trigger deferential review
on appeal. We affirm the judgment of the district court.

I. Factual and Procedural Background
  Plaintiff Leonard Lapsley worked for many years as a
millwright at the old Bethlehem Steel works in Burns
Harbor, Indiana. On May 19, 2004, Lapsley had just
finished filling a large spindle mechanism with
industrial strength grease, as he had many times before,
using a grease wand of his own manufacture. The
grease wand was connected by a hose to a pressurized
grease distribution system in the mill. Suddenly, as
Lapsley stood near the spindle, a loud “shotgun-like” bang
was heard across the mill floor and Lapsley fell to the
ground, covered in grease. Co-workers rushed to his
aid. He had a hole in his chest and could not breathe
properly. Lapsley was taken to the hospital, where it
was discovered that grease had somehow been in-
jected into his chest with enough force to break several
of his ribs, fill his chest cavity, and even create an exit
wound through his back. After eleven surgeries, doctors
have been unable to remove all of the grease, some
of which has fused with Lapsley’s internal tissues.
Lapsley survived, but he suffers constant pain so severe
4                                            No. 11-3313

that he is unable to return to work or do many activities
he once enjoyed. Leonard’s wife Barbara also sought
damages for the effect the accident has had on
their life together.
  The steel mill where Lapsley worked uses immense
rollers to flatten ingots of hot steel. Those rollers are
connected to drive motors by large drive shafts
known as spindles. Rather than try to explain the design
of a spindle with text alone, we include a diagram
taken from Xtek’s exhibits at trial:
No. 11-3313   5
6                                              No. 11-3313

  The drive end pod is turned by the mill’s powerful drive
motors. The spindle connects the drive end pod to the
roll end pod, which connects to and turns the heavy steel
rollers that flatten the steel ingots. Ring and hub gears
at each end transfer the rotational energy from the
motor to the spindle and then from the spindle to the
roller. The spring inside the spindle pushes both ends
of the spindle against a thrust plate. Keeping axial
tension in this way helps hold the spindle tightly in
place and limits its vibration as it turns. Because the
spindle weighs several tons, the spring must be very
powerful, exerting a lateral force of more than ten thou-
sand pounds.
   To reduce friction and wear, the gears at each end of
the spindle need to be kept lubricated, so the empty
spaces around each end of the spindle inside the end
pods are filled with industrial grease. Just before the
accident occurred, the spindle in question had been
returned from reconditioning by Xtek and had been
reinstalled. The roller was also installed in the roll end
pod but the spindle had not yet operated because it
needed to be greased. Lapsley filled the drive end pod
with grease through the port labeled “zerk fitting” in
the diagram above. He removed the actual zerk fitting
(a one-way valve) to aid that process. Lapsley next started
filling the roll end pod with grease. As the roll end had
filled, he went back to the drive end and was about
to replace the fitting there when he was hit in the chest
by the jet of grease.
  Hours after the accident the spindle was inspected
and was put into service. It operated for two years with-
No. 11-3313                                                   7

out any further incident. Both sides’ experts and an
internal team from the mill investigated possible causes
of the accident. No one was able to recreate it or to deter-
mine to an absolute certainty what was the precise cause.
  As Lapsley lay stunned on the floor of the mill being
helped by co-workers, he responded to the inevitable
question “What happened?” by gasping that the grease
wand had exploded. But witnesses testified that the
actual wand — which was admitted into evidence at trial
in pristine condition — had not exploded. In fact, the
wand was still connected to the hose leading to the mill’s
centralized, high-pressure grease distribution system.
Some inconsistencies in various witnesses’ memories
on this last point supported the hypothesis of Xtek’s
expert — that the jet of grease came from a pressurized
disconnection of the wand from the hose. Lapsley’s
lawyers and expert criticized the hose-disconnection
theory at trial. The jury did not accept it, and there
were ample reasons for that decision.1
  Lapsley’s expert, Dr. Hutter, hypothesized that the
internal spring must have become bound up or cocked

1
   In addition to the lack of any direct evidence of disconnec-
tion or damage to the grease wand or any other malfunction
in the grease distribution system, plaintiffs argued that a hose
disconnection would not have produced the explosive sound
heard across the mill. They also offered evidence that even
the small amount of grease highly pressurized in a clogged
wand would not have emerged as a jet, since incompressible
liquids expand only a small degree as pressure is dissipated.
We focus our further discussion only on the testimony of
plaintiffs’ expert challenged on appeal.
8                                               No. 11-3313

during reconditioning of the spindle or installation of
the roller. His theory was that the spring must have
suddenly let loose and expanded as the roll end pod
filled with grease, creating the loud explosive sound
heard across the mill and pushing the entire spindle
deeper into the drive end pod. Since the space between
the spindle and the drive end thrust plate was com-
pletely filled with incompressible grease, the spindle
would have acted like a ram, pushing the grease away
and out through any opening in the mechanism. Lapsley
just happened to be standing two feet in front of
the narrow, open grease port, which acted to focus the
immense energy from the spring into a narrow, high-
velocity jet of grease.
   The grease port was not the only opening through
which grease could escape under that pressure, but it was
probably the path of least resistance. The pod had relief
fittings, which would allow some grease to escape if the
internal pressure exceeded five pounds per square inch,
and rubberized “Glyd seals,” which would give way at
fifty to sixty pounds per square inch. Dr. Hutter ac-
counted for these alternate grease pathways in his cal-
culations. He still concluded that the effect of the spring
unbinding and acting as a ram could produce suf-
ficient grease velocity to cause Lapsley’s injuries. He also
calculated the possible effect of an alternative thrust
plate design — the design actually used by Xtek both
before and after the accident, but not with the spindle
involved in the accident. That alternative design had
grooves cut into it to assist grease flow throughout the
mechanism. Dr. Hutter’s calculations showed that those
grooves could have rerouted some flow and thereby
No. 11-3313                                             9

reduced the jet of grease out the grease port enough
to reduce significantly the injury to Lapsley.
   Long before trial, Dr. Hutter submitted a preliminary
report and was deposed by Xtek’s lawyers. The Lapsleys’
lawyers did not provide all of Dr. Hutter’s notes and
calculations supporting his report until the day of the
deposition. That is the sort of oversight that makes it
more difficult to take an effective deposition. It should
not have happened. But Xtek went forward with the
deposition as scheduled. The remedy for the late dis-
closure of notes and calculations was left to the district
court’s discretion, and the district judge reasonably
allowed Xtek to conduct a second deposition. See, e.g.,
Hunt v. DaVita, Inc., 680 F.3d 775, 780-81 (7th Cir. 2012)
(deferring to district court’s discretion in determining
whether to impose sanctions for improper deposition
tactics). The second deposition took place shortly before
trial. At the same time the court ordered the second
deposition, it also denied Xtek’s Daubert motion to
exclude Dr. Hutter’s testimony entirely. The court based
its decision on the preliminary report and calculations
that had been disclosed, and the initial deposition testi-
mony.
  In its Daubert motion, Xtek had argued that Dr. Hutter’s
proposed testimony lacked scientific basis. The district
court disagreed, pointing to the “commonly known
methodologies and physics calculations” that Dr. Hutter
used in reaching his conclusions. Those calculations
included the use of Bernoulli’s equation regarding
energy in moving fluids and reference to “widely
10                                           No. 11-3313

accepted factors concerning the force necessary to pene-
trate human skin.” The court concluded that because “the
principles upon which Hutter relied have long been
established and accepted within the scientific and engi-
neering community, both Hutter’s methodology and
his conclusions constitute admissible evidence.” The
court also found that the conclusions were relevant,
correctly ruling that defendant’s disagreement with
Dr. Hutter’s theory on causation could not be the sole
reason for excluding it.
  The district court also ruled on Xtek’s summary judg-
ment motions, granting summary judgment and dis-
missing plaintiffs’ claims for manufacturing defect and
failure to warn under Indiana law. The court held that
plaintiffs’ failure-to-warn claim failed as a matter of
law because there was no evidence of similar prior in-
cidents such that defendant should have been aware
of, and expected to warn of, the risk of grease ejection.
There was also no evidence of a manufacturing defect
in the spindle. The district court denied summary judg-
ment on plaintiffs’ design-defect claim, however, al-
lowing it to proceed to trial. The court found that
Dr. Hutter’s testimony about the alternative thrust plate
design raised a genuine issue of fact with regard to that
claim. Xtek argues on appeal that since a design-
defect claim also incorporates an element of foresee-
ability under Indiana law, the lack of evidence fatal
to the failure-to-warn claim should have doomed the
design-defect claim, as well. But as we explain below,
the argument overlooks Dr. Hutter’s testimony about
reasonable care in design. In the district court’s view,
No. 11-3313                                                11

that testimony foreclosed judgment as a matter of law,
and his testimony on that point simply was not chal-
lenged at trial.
  After a five-day trial, the jury returned a verdict of
$2.97 million against Xtek, after allocating 65 percent of
the fault for the accident to Xtek and 35 percent to the
mill owner, which was not a party. Represented by a
new team of lawyers, Xtek filed a Rule 50(b) motion
for judgment as a matter of law that asked the district
court to reconsider its refusal to exclude Dr. Hutter’s
testimony. The district court denied that motion, re-
ferring to its earlier ruling on the issue. Xtek has appealed.
  On appeal, Xtek objects to both the initial Daubert
ruling and the denial of its Rule 50(b) motion for judg-
ment as a matter of law. With regard to the Rule 50(b)
denial, Xtek does not argue that the evidence as
actually presented was insufficient to support the jury
verdict, but that it would have been insufficient
without Dr. Hutter’s testimony. Xtek argues again that
Dr. Hutter’s expert opinions regarding causation, alter-
nate design, and reasonable care or foreseeability lacked
scientific basis and should have been excluded by the
district court under Federal Rule of Evidence 702 and
Daubert. We disagree on all counts. The district court did
not abuse its discretion by admitting Dr. Hutter’s testi-
mony on each of these issues. In the face of that testi-
mony, Xtek was not entitled to judgment as a matter
of law. We discuss first the requirements of Daubert and
Rule 702 as applied to Dr. Hutter’s causation and
alternate design testimony, and finally the issue of
foreseeability.
12                                              No. 11-3313

II. Daubert and Causation
  Determining the true facts of a case often requires
“the application of some scientific, technical, or other
specialized knowledge.” Fed. R. Evid. 702, advisory com-
mittee’s note to 1972 proposed rules. Federal Rule of
Evidence 702 permits testimony by qualified experts
where such testimony will help the trier of fact under-
stand the evidence or decide the factual issues. As the
Rule 702 committee notes and Rules 703 to 705 make
clear, an expert may give an opinion to the jury con-
cerning the facts, subject to cross-examination on the
work forming the basis of that opinion, or may, less
frequently, “give a dissertation or exposition of scientific
or other principles relevant to the case, leaving the trier
of fact to apply them to the facts.” Id. Rule 702 requires
that expert testimony be relevant, reliable, and have a
factual basis — requirements that must be met before
the jury is allowed to hear and perhaps be persuaded
by the expert testimony. As the Supreme Court explained
in Daubert, the trial judge must make a determination at
the outset whether these factors are satisfied by the
proposed testimony. 509 U.S. at 592-93. Under Rule 702,
the trial judge stands as a gatekeeper to prevent
irrelevant or unreliable testimony from being admitted.
  Screening evidence pre-trial is a function squarely
within the purview of the trial judge. We review a
district court’s decision to admit or exclude expert testi-
mony for abuse of discretion, without substituting our
own judgment for the district judge’s exercise of discre-
tion. E.g., Kunz v. DeFelice, 538 F.3d 667, 675 (7th Cir.
No. 11-3313                                                13

2008). We review de novo, however, the district court’s
understanding and proper application of the multi-factor
Daubert framework. For example, in Metavante Corp. v.
Emigrant Savings Bank, 619 F.3d 748, 760 (7th Cir. 2010),
we applied de novo review where the court “failed to
perform a Daubert analysis” and articulated only a one-
sentence conclusion. See also Naeem v. McKesson Drug
Co., 444 F.3d 593, 608 (7th Cir. 2006) (declining to
apply deferential review where district court provided
no analysis of methodology in its one-sentence deter-
mination). Similarly, we refused to defer to a con-
clusory Daubert determination in Fuesting v. Zimmer, Inc.,
421 F.3d 528, 534-35 (7th Cir. 2005), modified on
rehearing on other grounds, 448 F.3d 936 (7th Cir. 2006),
though we repeated the general rule: “Provided the
district court adhered to Daubert’s parameters, we will
not disturb the district court’s findings unless they
are manifestly erroneous.”
   The parties here disagree about whether the district
court’s brief written analysis of Dr. Hutter’s testimony
was sufficient to justify deferential review. We find that
it was.
  Xtek relies heavily on ATA Airlines, Inc. v. Federal Express
Corp., 665 F.3d 882 (7th Cir. 2011), in which we found
erroneous the admission of a regression analysis that
was based on only the district court’s (correct) state-
ment that regression is a widely accepted method. In
fact, there were “grave questions concerning the reliabil-
ity” of the expert’s specific calculations. We noted that
neither side’s lawyers successfully conveyed their own
14                                              No. 11-3313

understanding of the regression analysis they were
arguing about. Id. at 889. As Lapsley points out, how-
ever, ATA Airlines did not change the standard of
review established in our cases for appeals from
Daubert decisions.
  The district judge here did more than state the general
acceptability of Dr. Hutter’s methods and calculations.
The judge provided specific examples that show he
reviewed and understood the basis for Dr. Hutter’s
conclusions. As our discussion below makes clear, the
math and science here are within the comprehension
of judges and lawyers without extraordinary assistance.
Xtek disputes the completeness and therefore the
relevance of Dr. Hutter’s calculations, but it has not
identified, and we have not detected, any grave ques-
tions about the reliability of the calculations actually
performed by Dr. Hutter. Under these circumstances,
the district court’s brief application of the Daubert frame-
work is sufficient to warrant the deferential review we
give it below.
  The Rule 702 inquiry is fact-dependent and flexible.
See Kumho Tire, 526 U.S. at 141 (“[A] trial court
may consider one or more of the more specific factors
that Daubert mentioned when doing so will help
determine that testimony’s reliability. But, as the Court
stated in Daubert, the test of reliability is ‘flexible,’
and Daubert’s list of specific factors neither necessarily
nor exclusively applies to all experts or in every
case.”) (emphasis in original). The non-exclusive list of
Daubert reliability factors for scientific evidence includes
No. 11-3313                                               15

whether or not the theory or technique has been (1) tested,
(2) subjected to peer review and publication, (3) analyzed
for known or potential error rate, and/or is (4) generally
accepted within the specific scientific field. Daubert, 509
U.S. at 593-94. The purpose of the inquiry is to vet the
proposed testimony under Rule 702’s requirements that
it be “based on sufficient facts or data,” use “reliable
principles and methods,” and “reliably appl[y] the princi-
ples and methods to the facts of the case.” Fed. R. Evid.
702. As the Supreme Court instructed in Kumho Tire,
see 526 U.S. at 152-53, we “give the district court wide
latitude in performing its gate-keeping function and
determining both how to measure the reliability of
expert testimony and whether the testimony itself is
reliable.” Bielskis v. Louisville Ladder, Inc., 663 F.3d 887,
894 (7th Cir. 2011).
  On appeal, Xtek argues that none of the reliability
factors are satisfied by Dr. Hutter’s opinions or the cal-
culations underlying them. Xtek asserts that the
opinions are “not science” because they were not physi-
cally tested, peer reviewed or published, or subject to
the other factors. We disagree. Dr. Hutter applied reli-
able science to the known facts using well-established
methods. The physics principles used by Dr. Hutter were
published centuries ago by some of the most famous
names in science, and those principles have been used
and tested (i.e., peer reviewed) by physicists and engineers
for centuries. Dr. Hutter’s mathematical models (a form
of test) appear to be well-grounded in the facts and
data available. If some of his simplifying assumptions
failed to consider significant factors, such potential
errors went undetected and unchallenged at trial.
16                                            No. 11-3313

Dr. Hutter’s approach, starting from the known facts
about the accident and eliminating other possible ex-
planations (in this case, other possible sources of high
velocity grease) until he was left with a hypothesis
that was physically possible and that fit the evidence, is
a good example of the scientific method.
  Xtek also faults Dr. Hutter for not providing a
sufficient explanation of his calculations. Xtek argues
that these opaque calculations render his ultimate con-
clusions merely conclusory, and that unsupported opin-
ions have no place at trial. Rule 705 provides that
“an expert may state an opinion — and give the reasons for
it — without first testifying to the underlying facts or
data.” Disclosure of the underlying facts or data may be
left to cross-examination, and of course, an expert
who plans to testify to an opinion must make the basis
of that opinion available for evaluation by the court
and opposing parties. Once evaluated and deemed suf-
ficiently reliable for admission, that expert opinion is
submitted to the “capabilities of the jury and of the
adversary system generally.” See Daubert, 509 U.S. at 596
(rejecting an “overly pessimistic” view of these capabili-
ties).
   We do not agree that Dr. Hutter’s method and calcula-
tions were insufficiently detailed or inherently opaque
to the district court or the lawyers here. We do not find,
and the district court did not find, Dr. Hutter’s analysis
to be as difficult to understand as Xtek suggests. Lawyers
and judges who were not trained in science can benefit
from the famous “Two Cultures” lecture given in 1959
by British scientist and novelist C. P. Snow, in which
No. 11-3313                                               17

he described the cultural gap between persons schooled
in the sciences and those schooled in the humanities:
   A good many times I have been present at
   gatherings of people who, by the standards of the
   traditional culture, are thought highly educated and
   who have with considerable gusto been expressing
   their incredulity at the illiteracy of scientists. Once
   or twice I have been provoked and have asked the
   company how many of them could describe the
   Second Law of Thermodynamics. The response was
   cold: it was also negative. Yet I was asking some-
   thing which is about the scientific equivalent of:
   Have you read a work of Shakespeare’s?
Law must apply itself to the life of a society driven more
and more by technology and technological improve-
ments. Judges and lawyers do not have the luxury
of functional illiteracy in either of these two cultures.
Sometimes, as in this case, effective presentation, cross-
examination, and evaluation of expert testimony re-
quire lawyers and judges to fill in gaps in their scientific,
engineering, or mathematics educations or refresh their
memories about them. We see no indication, either
from the district court’s Daubert ruling or its later dis-
cussions of the expert evidence during trial, of any defi-
ciency in the court’s preparation or in its understanding
of the proposed evidence.
  Dr. Hutter’s calculations to support his theory of causa-
tion were attached to his report and made available to
Xtek’s counsel and the district judge prior to his ruling
on Xtek’s initial Daubert motion. Those calculations
18                                           No. 11-3313

apply principles of classical mechanics commonly
taught in high school physics classes. His notes, mis-
takenly disparaged by Xtek as “the instructive
equivalent of Sanskrit,” are in fact relatively straight-
forward to comprehend for those familiar with these
basic mechanical principles and with the rudiments of
scientific notation. If they appear opaque to some
readers, it is more likely because of the “Two Cultures”
problem rather than any inadequacy of presentation. As
with most informal work-product, the notes could have
been even clearer and more self-explanatory, but Xtek’s
lawyers and the district judge all had opportunities to
ask Dr. Hutter to explain his calculations. Based on
the written submissions, the district judge here did not
feel the need to question Dr. Hutter directly, and Xtek
did not request that he hold a hearing to do so.
  The page of notes that was selected by Xtek as an exam-
ple of Dr. Hutter’s scientific “Sanskrit” is reproduced
below:
No. 11-3313                                           19

  The basic equations of classical mechanics used in this
case by both sides’ experts were first published in 1687
by Sir Isaac Newton in his Philosophiæ Naturalis
20                                                   No. 11-3313

Principia Mathematica.2 The Principia, which built on the
work of Galileo and Descartes, and on Newton’s own
development of calculus, is often described as the most
significant scientific publication of the Western world. It
contains Newton’s Second Law of Motion, relating the
force (F) on an object to the product of its mass (m) and
acceleration (a). This equation is commonly expressed as:
F = ma. Acceleration is defined as the rate of change (or
derivative in calculus terms) of the velocity (v) over time
(t). These relationships, discovered by Newton, led to the
derivation of equations like the kinetic energy equation,
which in turn allows the determination of velocity
when force, distance, and mass are known.3
  Kinetic energy is the energy stored in an object that is
in motion. Gottfried Leibniz and Johann Bernoulli devel-
oped the principle, building on Newton’s mechanics. The

2
  For the curious, Newton’s personally annotated copy of the
Principia first edition has been digitized by the Cam-
bridge Digital Library and is available online at http://
cudl.lib.cam.ac.uk/collections/newton (last visited July 24, 2012).
The original text is in Latin, but innumerable explanations
and translations are available in libraries and online.
3
  In the centuries since publication of the Principa, only a few
exceptions have been found for Newton’s Second Law. Einstein
discovered that as velocity nears the speed of light, corrections
need to be made to account for effects of special relativity.
Also, there are complications at the extremely small scale
of quantum mechanics. Newtonian physics still provides a
reliable and workable description for the mechanical systems
of a steel mill.
No. 11-3313                                                     21

best known equation for kinetic energy (E) is expressed
as one-half the product of the mass (m) and the square
of the velocity (v): E = ½ mv 2 . This equation appears on
the “Sanskrit” example page of Dr. Hutter’s calcula-
tions and is a direct application of Newton’s Second Law.
First Dr. Hutter calculated the assumed Energy from the
spring — that is, the work done by the spring exerting
10,550 pounds (#) of force over an assumed distance of
0.37 inches ("). Because the fundamental law of conserva-
tion of energy tells us that total energy is conserved
(neither gained nor lost) in a closed system, Dr. Hutter
could treat the work done by the spring at one end of
the mechanism as the eventual kinetic energy imparted
to the grease that exited the spindle. 4 Inputting that
known energy, and the mass of the grease thought
to be involved, the kinetic energy equation yielded a
theoretical grease velocity of 145.3 feet per second, which
Dr. Hutter also converted to 1744 inches per second and
99 miles per hour.
 Another important equation on the “Sanskrit” page,
P = ½ D v 2 , relates the dynamic pressure (P) to one-half

4
   In fact, some small amount of energy was certainly lost to
heat from friction and to turbulence in the grease as it moved
inside the mechanism. As is common and acceptable in mathe-
matical modeling and estimation, Dr. Hutter assumed that
these effects were so small in relation to the total energy that
they could be ignored without compromising the end result.
If Xtek believed the effects of friction were actually significant,
it could have cross-examined Dr. Hutter on that point or
introduced its own evidence to counter his estimates.
22                                              No. 11-3313

the product of the fluid density (D ) and the square of the
fluid velocity (v). This is one form of Bernoulli’s equation,
a fundamental principle of fluid dynamics first pub-
lished by mathematician Daniel Bernoulli (son of Johann)
in 1738 in his book Hydrodynamica. Bernoulli’s equation
in its various forms has innumerable applications in
aerodynamics (it describes how the shape of an air-
plane’s wing lifts the plane or an inverted wing
keeps a race car on the track in a high-speed turn) and
in hydraulics. Dr. Hutter used the equation here to
convert the velocity of the grease, which he had derived
from the kinetic energy equation, into a pressure value
of approximately 140 pounds per square inch (psi).
Published results of experiments with jets of fluid taught
that pressures above 100 psi could pierce clothing and
human flesh.
  So, starting from the assumed values (which were
reasonable estimates from the information available) for
the force of the spring, the distance it may have traveled,
and the density and mass of the grease, Dr. Hutter was
able to confirm the theoretical possibility that a sudden
release of tension in the spring could produce a high
velocity jet of grease at the other end of the mechanism —
one moving with sufficient energy to create sufficient
pressure to cause Lapsley’s wounds. Dr. Hutter con-
cluded, and testified, that the spring probably caused
the accident, suddenly ramming the spindle into the
full grease reservoir with enough force to create the
dangerous jet of grease. This conclusion was based in
large part on Dr. Hutter’s conclusion that there was no
other viable explanation for Lapsley’s injuries, including
No. 11-3313                                            23

specifically that the available evidence was not con-
sistent with the steel mill’s internal grease distribution
system causing the accident.
  Dr. Hutter could not say exactly how the spring got
bound up or cocked and then released. From this gap,
Xtek argues that his theory is incomplete and there-
fore amounts to impermissible conjecture. Dr. Hutter
was cross-examined on this point and testified that the
accident itself — other sources of great pressure having
been excluded — was evidence that the spring was the
cause. He testified that the spring could have become
cocked in the spindle assembly or installation process.
However it got bound up, Dr. Hutter’s calculations
showed that the release of the spring, traveling as little
as 0.37 inches, could have created the necessary force.
Rule 702 asks whether Dr. Hutter’s causation hypothesis
was reliably supported and applied to the known facts,
such that it rises above speculation and becomes a pre-
sentable probability. See Smith v. Ford Motor Co., 215
F.3d 713, 718-19 (7th Cir. 2000) (hypothetical explana-
tions of probable causes permitted where they have
“analytically sound bases” beyond mere speculation). Even
when judging sufficiency of all the evidence, Indiana
design defect law does not require absolute certainty on
every aspect of causation. The plaintiff need only
present “evidence of probative value based on facts, or
inferences to be drawn from the facts” that rises above
“supposition or speculation.” Smith v. Beaty, 639 N.E.2d
1029, 1033-34 (Ind. App. 1994) (expert opinion that some-
thing is “possible” may be sufficient to sustain verdict
in conjunction with totality of other circumstantial evi-
24                                                    No. 11-3313

dence). The district court did not abuse its discretion
in concluding that the proposed causation testimony
was reliable.5
  Dr. Hutter’s report, calculations, and deposition testi-
mony available to the district court at the time of Xtek’s
Daubert motion were clear and understandable, at least
on their face. When the relevant question on appeal
is whether the district court reasonably found the pro-
posed evidence reliable, we need not further evalu-
ate Dr. Hutter’s math for all possible substantive errors.
That is what the adversary process, including cross-
examination at trial, is for. Throughout this litigation,
no one has attacked or questioned the calculations
we described above, and we see no fault in them. If
there were pertinent attacks to be made, the proper time
to have done so was no later than trial.

5
   Xtek makes several arguments on appeal going to the weight
and ultimate truth of the evidence rather than its Rule
702 reliability. For instance, Xtek argues that its engineer,
Mohammed Daher gave “uncontradicted” testimony that if the
spring were to be bound up, the rollers could not have been
installed because they would “fall out.” The diagrams that Xtek
showed the jury seem to belie the possibility that a half-inch
play in the internal spring would be enough to allow the heavy
mechanism, which per Daher is externally supported during
installation, to fall to pieces. Daher also testified that installa-
tion of the rollers can cause the spring to be pushed in. If we
were examining sufficiency, we could say that the jury may
have reasonably concluded, as Dr. Hutter opined, that this
was when the spring probably became cocked.
No. 11-3313                                              25

III. Alternative Design
  Just before the accident, after many years of using thrust
plates with grease grooves around their outside edges,
Xtek substituted a new thrust plate design that omitted
those grooves. As Xtek’s engineer Daher testified, the
grooves were designed to facilitate grease flow through-
out the end pod mechanism when filling it with grease
from outside the pod, as Lapsley was doing. Daher testi-
fied that the grooves were removed in the new design
because they were not needed to spread grease when
using the new method of filling the pod through the
spindle itself. Several months after the accident, Xtek
went back to the thrust plates with grooves. According
to Daher, this was done in case millwrights continued to
grease through the outside port, as they had always
done before the design change.
  Dr. Hutter employed simple calculations using the
areas of the corresponding exit paths to show that the
grooves would have significantly lessened the grease
exit velocity and pressure by providing more alternate
paths for the grease to escape. Dr. Hutter started from
calculations similar to those discussed above to
estimate the energy and velocity of the shifting spindle,
which acted across a wide area of the internal grease
reservoir. He then computed: (1) the much higher
velocity of the displaced grease if it had all exited
through the small area of the grease port, (2) the some-
what lower velocity if the additional exit area of the
available relief valves and Glyd seal were considered,
and (3) the much lower velocity if the additional exit
26                                               No. 11-3313

area of the grease grooves were available. Again em-
ploying Bernoulli’s equation, the calculations yielded
corresponding pressures in the thousands of pounds
per square inch without the grease grooves, and less
than a hundred pounds per square inch with them. For
reference, Dr. Hutter cited medical journal articles about
water-jet scalpels used to perform surgeries, which
operate in the range of several hundred to two thousand
pounds per square inch of water jet pressure. He con-
cluded that the grease grooves could have reduced the
jet of grease from the port from a surgical pressure to
a much safer one.
  Indiana law requires that proposed alternative designs
be shown to be cost-effective and able to reduce the
injury. See Pries v. Honda Motor Co., 31 F.3d 543, 545-46 (7th
Cir. 1994), citing Miller v. Todd, 551 N.E.2d 1139, 1141-42
(Ind. 1990). Expert testimony is not needed to show
the cost-effectiveness of a design actually used by the
defendant both before and after the accident. With
regard to reducing or preventing injury, Dr. Hutter’s
calculations modeled the effectiveness of the grooves at
reducing the grease velocities below skin-penetrating
pressures. Xtek raises the same arguments concerning
failure to explain and lack of absolute certainty that we
discussed above with regard to causation. They fail
here for the same reasons.
  Xtek also faults Dr. Hutter for failing to do physical
tests of his theories with regard to causation (the effect
of the spring releasing) and alternate design (the reduc-
tion in pressure from the grease grooves). Xtek calls
No. 11-3313                                               27

Dr. Hutter’s mathematical models the simulation of
science, not science. Testing is certainly one of the most
common and useful reliability guideposts for a district
court when contemplating proposed Rule 702 evidence.
But physical re-creations of industrial accidents are not
always feasible or prudent. See Schmude v. Tricam Indus-
tries, Inc., 556 F.3d 624, 626 (7th Cir. 2009) (discussing a
failed and potentially dangerous attempt to recreate a
ladder fall for a jury). Xtek’s argument also overlooks
the fact that simulation is one of the most common
of scientific and engineering tools. Around the world,
computers simulate nuclear explosions, quantum mech-
anical interactions, atmospheric weather patterns, and
innumerable other systems that are difficult or impossible
to observe directly. A mathematical or computer model
is a perfectly acceptable form of test.
  We do not require experts to drop a proverbial apple
each time they wish to use Newton’s gravitational
constant in an equation. Similarly here, the burden of
proof at trial, and certainly the guideposts of reliability
attached to the Daubert inquiry, did not require Dr. Hutter
to try to recreate the binding up of a ten thousand
pound spring to produce a potentially deadly jet of in-
dustrial grease. Xtek was free to raise the lack of physical
tests of the accident with the jury, and to attack any aspect
of the mathematical model that was used in place of
physical re-creations. The district court, however, did
not abuse its discretion by allowing Dr. Hutter to testify
to the results of his mathematical simulations.
28                                                No. 11-3313

IV. Foreseeability
  Xtek argues most strenuously on appeal that Dr. Hutter’s
opinion about reasonable care in design (which in-
cludes an element of foreseeability under Indiana law)
is merely conclusory and therefore should not have
been allowed before the jury. Among all of Dr. Hutter’s
opinions, this one certainly had the least support from
data, but it was also completely unchallenged by Xtek
during the trial. On appeal, Xtek now seeks to exclude
what it did not challenge at trial. We do not find an abuse
of discretion in allowing Dr. Hutter to opine about fore-
seeability.
  In addition to proving causation in fact and demon-
strating a reasonable alternative design, Indiana design
defect law requires plaintiff to show that the defendant
failed to exercise reasonable care in designing the prod-
uct. Ind. Code § 34-20-2-2; TRW Vehicle Safety Systems, Inc.
v. Moore, 936 N.E.2d 201, 209 (Ind. 2010). This reasonable
care standard imports “general negligence principles.” See
Pries, 31 F.3d at 545; Whitted v. General Motors Corp., 58 F.3d
1200, 1206 (7th Cir. 1995). Those principles include an
element of proximate cause, which “turns largely on
whether the injury ‘is a natural and probable consequence,
which in the light of the circumstances, should have been
foreseen or anticipated.’ ” City of Gary ex rel. King v. Smith
& Wesson Corp., 801 N.E.2d 1222, 1244 (Ind. 2003), quoting
Bader v. Johnson, 732 N.E.2d 1212, 1218 (Ind. 2000).
 Before trial, Dr. Hutter’s report asserted his opinion,
based on his calculations and observations of the
various thrust plates, that a safer design existed. He also
No. 11-3313                                            29

asserted that Xtek, as the mechanism’s sole designer
and manufacturer, should have known of the defective
condition created by the thrust plate redesign. The
district court, in its denial of Xtek’s initial Daubert
motion, found this evidence “relevant in establishing
that alternative designs existed and that the Defendant
should have used them.” Xtek had objected, in the
separate context of the failure-to-warn claim, that
Dr. Hutter provided no reports or evidence of similar
accidents that could have informed Xtek of a potential
grease ejection hazard. But reports of prior incidents
are only one way to establish that a defendant in a
design defect case should have known of a hazard. If
prior events were the only possible basis, defendants
could escape liability for genuine defects by pointing to
the unusual and thus arguably unforeseeable features
present in every accident. Dr. Hutter, a highly qualified
mechanical engineer with a career focused on safety in
design, testified in essence that a reasonable designer
would have thought about the possibility of the power-
ful internal spring pushing the spindle — and would
have considered the consequences that would arise.
His assertions about what a reasonable thrust plate
designer should contemplate might be vulnerable to
criticism, but Xtek did not lay a glove on that opinion
in the adversarial testing of the jury trial. The district
court found the opinion was relevant and reliable
enough to pass Rule 702, and we see no abuse of discre-
tion in that finding.
  Dr. Hutter testified that designers of equipment like
this possess the knowledge and expertise to identify
30                                            No. 11-3313

hazards, and that the presence of a spring with over ten
thousand pounds of force should have led Xtek’s
engineers to evaluate this particular kind of hazard.
Expert testimony by engineers concerning what an ordi-
nary engineer would understand and do is common-
place in patent law. It is naturally relevant to the
foreseeability question here as well. See Vaughn v.
Daniels Co. (West Virginia), Inc., 841 N.E.2d 1133, 1137
(Ind. 2006) (applying Indiana evidence rules and
allowing expert to opine about reasonable care based
on his “engineering and construction management ex-
pertise”). As the district court noted in its Daubert
ruling, Xtek did not dispute Dr. Hutter’s engineering
qualifications. Those qualifications provide the primary
basis for his testimony about what a similarly qualified
design engineer might anticipate.
  Unlike the opinions discussed above, no one needs to
understand physics to counter design evidence ef-
fectively or to criticize it as dependent on hindsight
bias. “Vigorous cross-examination, presentation of con-
trary evidence, and careful instruction on the burden
of proof are the traditional and appropriate means of
attacking shaky but admissible evidence.” Daubert, 509
U.S. at 596. “These conventional devices, rather than
wholesale exclusion under an uncompromising
‘general acceptance’ test, are the appropriate safe-
guards where the basis of scientific testimony meets
the standards of Rule 702.” Id.
  Xtek failed to counter Dr. Hutter’s brief but admissible
testimony on the question of whether grease ejection was
No. 11-3313                                                      31

foreseeable to designers of the spindle assembly. In fact,
the only people who used the words “foresee” or “foresee-
able” in front of the jury during trial were plaintiffs’
lawyer, when asking Dr. Hutter if he thought the
designers could have foreseen a dangerous condition
(he said yes), and the judge, when properly instructing
the jury on Indiana law concerning design defects.
Dr. Hutter was not even cross-examined on his opinion
about the reasonable care of the designers. Xtek’s
engineer and expert both testified. Neither provided
even a contrary opinion on the issue, and Xtek opted not
to remind the jury of the issue during its closing argu-
ment. We see no persuasive reason to hold now
that Dr. Hutter’s evidence on the issue should have
been excluded.6

6
   Xtek suggests that if we were to agree that Dr. Hutter’s
testimony should have been excluded, the proper remedy would
be an outright dismissal for insufficiency of the evidence rather
than a remand for a new trial. Other circuits have remanded
for retrial in analogous circumstances, leaving district judges
substantial discretion in reaching a fair solution when a party
presented his case at trial relying on a decision to admit evi-
dence that turned out to be erroneous. See, e.g., Tamraz v. Lincoln
Elec. Co., 620 F.3d 665, 677 (6th Cir. 2010); Dodge v. Cotter Corp.,
328 F.3d 1212, 1229 (10th Cir. 2003). Defendant’s proposed
dismissal remedy could be manifestly unfair to parties who
based their trial strategy on the district court’s pre-trial eviden-
tiary rulings — particularly in cases where the defendant failed
to attack the sufficiency of the evidence during trial. Plaintiffs
who seemed to have met their evidentiary burden might have
found other ways to meet that burden if they had known
                                                      (continued...)
32                                               No. 11-3313

                             * * *
  The accident that disabled Leonard Lapsley appears
to have been unprecedented, and fortunately it has not
been repeated with other millwrights. The uniqueness
of an accident can weigh against jury findings of
foreseeability and lack of reasonable care in design,
but that is a matter for the jury to decide. The jury here
accepted Dr. Hutter’s uncontradicted expert opinion
that a reasonable designer would have considered
the danger of the powerful spring being bound up unex-
pectedly and releasing its energy so as to act like a ram
on the grease in the spindle assembly. Rule 702 provides
a test of reliability, not of ultimate merit. District
courts acting as gatekeepers of scientific, technical, or
specialized knowledge evidence retain significant dis-
cretion under the flexible Daubert inquiry. The district
court here did not misapply Daubert, and Xtek has identi-
fied no compelling reason to disturb the court’s exer-
cise of its discretion.
    The judgment of the district court is A FFIRMED.

6
   (...continued)
they would not be allowed to present key part of the testimony
of their chosen expert witness. We need not and do not decide
this question, just as we declined to decide it in Fuesting
v. Zimmer, 448 F.3d 936, 939 n.1 (7th Cir. 2006).

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