The child spits out the thermometer after 60 seconds. The reading is 101 degrees. More likely than not, most people would agree, the child has a fever. The methodology of the thermometer is well-known. The incompleteness of the test would not invalidate the knowledge or the methodology.
Every scientific method known to humanity is subject to error, both mechanical and human.
The best way of running a breathalyzer is to have a period of observation of the subject fifteen minutes before the test, to have blank tests preceding each of two actual tests, and to run a control test following the actual test. Dubowski, supra, at 308. Omission of these safeguards lowers the reliability of the tests, it does not eliminate them as scientific aids to a factfinder investigating drunkenness. As the defense pointed out at trial, Sierra, the operator of the machine, could have been mistaken in saying that he saw a reading of .15. The possibility was appropriately explored by cross-examination.