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5. Example collimation check

Instrument used has a stadia multiplier of 100; rod units are feet.

A baseline was laid out with a cloth tape using an interval of approximately 75 feet.


Instrument set up at point 1

Sight rod on A

Read and record the three crosshairs. g ex 1

Reduced readings:

Average should be close to the middle reading, if not, then one or more readings incorrect; re-read.

Check: d1A should be approx 75 ft, same as interval.

g ex 2

 

It's important to reduce the readings immediately after taking them. The computations help identify if a reading error has been made. If there is an error, the equipment is still in place so the measurements can be quickly redone.

Sight rod on B

Read and record the three crosshairs. g ex 3

Reduced readings

Average should be close to the middle reading, if not, then one or more readings incorrect; re-read.

Check: d1B should be approx 150 ft, twice the interval.

g ex 4

 

 The instrument is moved to Point 2 and the process repeated.The readings and computations are:

Sight rod on A

g ex 5

Sight rod on B  

g ex 6

  

Compute the error and distance from Equations G-1 and G-5:

g ex 7

A negative error indicates theLoS is below horizontal.

g ex 8

Using Equations (G-2) and (G-3) express collimation error as a ratio and angle:

g ex 9

g ex 10

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