Version 1 

September 30, 2004 

 

ATTACHMENT X

BENCH MARK TIES 

TO 

SCOPE OF WORK FOR SHORELINE MAPPING 

UNDER THE 

NOAA COASTAL MAPPING PROGRAM 

REMOTE SENSING DIVISION 

NATIONAL GEODETIC SURVEY 

NATIONAL OCEAN SERVICE 

NATIONAL OCEANIC & ATMOSPHERIC ADMINISTRATION 

U.S. DEPARTMENT OF COMMERCE
X – Page 2 

TABLE OF CONTENTS 

ATTACHMENT X: BENCH MARK TIES PAGE 

 

1. INTRODUCTION........................................................................... 3 

2. SINGLE MARK LEVEL TIE (3RD ORDER)...................................................... 3 

3. OBSERVING SEQUENCE FOR CONVENTIONAL LEVEL...................... 3 

4. OBSERVING SEQUENCE FOR DIGITAL LEVEL................................... 5 

 

5. DATA SUBMISSION....................................................................... 6 

ANNEX 1: OBSERVATIONS FOR BENCH MARK TIES BLANK FORM.......... 7 
X – Page 3 

ATTACHMENT X: BENCH MARK TIES 

1. INTRODUCTION 

The purpose of these guidelines is to provide the information necessary to transfer an elevation 

from an existing NAVD88 benchmark that cannot be used for GPS observations to a nearby GPS 

station. The two stations must be “closeby” which is defined here as no more than four “set-ups” of 

the level instrument. 

2. SINGLE MARK LEVEL TIE (3RD ORDER) 

An assumed elevation for the bench mark can be used in the leveling since the principal concern is 

with the difference of elevation between the bench mark and the GPS station. It should be noted 

that the published elevation of the GPS station would only be published to the nearest centimeter. 

This is because the absolute elevation of the bench mark cannot be verified without incorporating 

other bench marks into the survey as a check. Many projects do not provide the resources required 

for this multiple mark check, but it is still imperative that the GPS station have the best precision 

allowable. 

Record rod readings to millimeters or hundredths of feet. The model and type of instrument and 

rods (e.g., fiberglass, aluminum, single piece, etc.) as well as rod scale units (e.g., meters, feet, or 

bar code) should be entered on the “Observations of Bench Mark Ties” form where indicated. See 

Annex 1.

3. OBSERVING SEQUENCE FOR CONVENTIONAL LEVEL 

1. Remove equipment from travel cases, attach level instrument to tripod, and let equipment 

acclimate to local conditions. Perform instrument check per the manufacturer’s instructions. Set up 

the instrument about halfway between the stations, but no more than 70 m (230 ft) away from either 

point or from one of the points and a turning pin in the case of multiple setup requirements. Backsight 

distance to foresight distance imbalance shall be less than 5 meters. Accumulated backsight to 

foresight distance imbalance shall be less than 10 meters in the case of multiple setups. 
X – Page 4 

Figure 1. Direct old mark to new mark level tie. Note: Backsight-foresight distance imbalance 

should be less than 5 meters. 

2. Plumb the level rod on the highest point of the old mark. Let’s call the old mark M 123. Record 

the designation of the point and its published elevation noting the reference vertical datum and units 

of measure. 

Figure 2. Old mark to new mark level tie for distances over 140 m. Note: Accumulated 

backsight-foresight setup imbalance should be less than 10 m. 

3. Backsight Reading: Observe the intercept of the middle reticule of the rod scale as backsight 

reading. Record the rod reading to the nearest millimeter (or hundredths of a foot) as indicated 

above. Record the stadia reading to determine distance from the point to the instrument. 

4. Compute height of instrument, HI, which is the sum of the backsight and the published elevation. 

5. Plumb the rod on the highest point of the new bench mark. Record the designation of the new 

mark, e.g., M 123 RESET, or TP1 (for turning point 1 in the case of multiple setups). 

6. Foresight Reading: Observe the intercept of the middle reticule of the rod scale as foresight 

reading. Record the stadia reading to determine distance from the point to the instrument. 
X – Page 5 

7. Compute the elevation of the new point, new bench mark, or turning point, which is the difference 

of the HI minus the foresight. 

8. Reset and re-level the instrument. Level backward from the new point to the old, in the same 

manner as steps 2 through 7. 

Note: The elevation computed for the old point as a result of the backward leveling may differ by no 

more than +/-12D (where D is the shortest length of section in kilometers one-way) from the 

published elevation. 

9. To compute the elevation difference from the old mark to the new, subtract the mean of the two 

elevations for the old mark from the elevation for the new mark. 

4. OBSERVING SEQUENCE FOR DIGITAL LEVEL 

These observing procedures are intended for use with digital levels. 

1. Remove equipment from travel cases, attach level instrument to tripod, and let equipment 

acclimate to local conditions. Perform instrument check and adjustment as outlined in the digital level 

manual. 

2. Set up the instrument about halfway between the stations. Limit sight lengths to no more than 70 m 

(230 ft) from either point or from one of the points and a turning pin in the case of multiple setup 

requirements, e.g., distance between points is greater than 140 meters. Backsight distance to foresight 

distance imbalance shall be less than 5 meters. Accumulated backsight to foresight distance 

imbalance shall be less than 10 meters in the case of multiple setups. 

3. Level up the instrument using the three foot screws while observing the bulls-eye bubble. Turn on 

the instrument and select the backsight/foresight level program. Confirm that you want to start then 

enter the starting elevation for the old mark. Set and confirm instrument parameters, e.g., meaning 3 

measurements, display maximum decimal places, record readings to onboard module, and observing 

configuration, such as rod type, and metric units. 

4. Plumb the level rod on the highest point of the old mark, e.g., domed top of disk M 123. Record 

the designation of the point and its published elevation, noting the reference vertical datum and units 

of measure. 

5. Backsight Reading: Point using the vertical crosshair of the level instrument on the middle of the 

rod over the old mark and use the focusing knob to bring the image of the rod into sharp focus 

Depress the measure button and record the rod reading. Note distance from rod to instrument. It 

should be less than 70 meters. 

6. Plumb the rod on the highest point of the new bench mark. Record the designation of the new 

mark, e.g., M 123 RESET, or TP1 (for turning point 1 in the case of multiple setups). 

7. Foresight Reading: Point and focus the level instrument on the rod over the new mark. Depress the 

measure button and record the rod reading. Note distance from rod to instrument. It should be less 

than 70 meters. Note imbalance between backsight and foresight distances. This difference shall be 

less than 5 meters. 
X – Page 6 

8. The elevation of the new bench mark or turning point is computed as the sum of the backsight 

reading and the published elevation minus the foresight reading. 

9. Reset and re-level the instrument. Level backward from the new point to the old, in the same 

manner as steps 2 through 7. Use the elevation determined from the forward leveling as the starting 

elevation for the backward leveling. The elevation computed for the old point as a result of the 

backward leveling may differ by no more than +/- 12D (where D is the shortest length of section in 

kilometers one-way) from the published elevation. 

10. To compute the elevation difference from the old mark to the new, subtract the mean of the two 

elevations for the old mark from the elevation for the new mark. The elevation for the new bench 

mark will be this computed difference, mean of both forward and backward leveling, plus the 

published elevation of the old bench mark. 

5. DATA SUBMISSION 

The following shall be supplied by the submitting office: 

1. Completed “Observations for Bench Mark Ties” form. See Annex 1. 

2. Digital Levels: Paper as well as digital copy of leveling observations. 
X – Page 7 

ANNEX 1: Observations for Bench Mark Ties 

Original Mark Stamping: PID (if known): Elevation: (ft / m) 

Datum: NGVD 29 or NAVD 88 (circle one) 

Replacement Mark Stamping: Date of Leveling: Computed 

Elevation: (ft / m) (from below) 

State: County: Latitude: N Longitude: W Datum: 

Leveling Equipment: Manufacturer Model Number Serial Number Level Instrument: Rod # 1: Rod # 2 (optional): Rod Scale 

Units: 

Point Backsight H.I. Foresight Elevation Length (ft/m) Remarks 

Forward Running: Old to New 

 

 

Backward Running: New to Old 

 

 

 

Agency / Firm: ________________________________________________ Signed: _____________________________ 

Address: ______________________________________________________ Telephone: ( ) _______________________ 

City / State / Zip: E-mail: