Lab: Level Testing

Objective: The objective of this lab is to determine the C-Factor, the collimation error, and to explore the randomness of a level

Overview: Determining the C-Factor will help eliminate the systematic errors associated with the level when the distance between the foresight and backsight is unbalanced. This factor will be applied to each measurement in order to obtain the truest value possible.

Equipment: The following is the equipment needed to perform this lab: an automatic level, tripod, level rod, turn points.

1. Perform a Peg Test on the level:

Follow the procedure outlined in lecture. Select two points (pegs) about 300 ft apart. Set up half way between, read both rods, calculate the True Difference in Elevation (TDE). Set up near A, read near rod A and far rod B. Apply TDE to near rod A reading (errorless) to compute "perfect" far rod reading. Subtract perfect far rod from actual far rod. Express C as slope of the line of sight ft/ft ratio. The sign = + if below the perfect, - if above.

You should repeat the procedure to be certain you get the same C factor within a reasonable range.

2. Test the randomness of your level.

Erect a level rod about 300 ft away from the instrument. Read the rod as precisely as you can (estimate last digit between least rod divisions). While looking through the level, gently tap the side of the level to dislodge the compensator. You should see the line of sight bounce up and down and eventually settling down stationary. Read the rod again. Do this repeatedly to gain a sample of 20 rod readings. Take the standard deviation, reject outliers, to get a good random sample. This is the +/- randomness of the compensator.

3. Test the "range of compensation" of your level.

Use the same rod as in #2. Align the telescope over one leveling screw, that screw should be pointed toward the rod. While looking through the telescope and gently tapping the telescope, turn the single screw one direction. Observe that the line of sight is "bouncing" with each tap. Eventually you will turn the level screw far enough one direction until the compensator "pegs" at the limit of its motion. Take a rod reading at this place.

Then turn the level screw the other direction until the compensator "pegs" at its limit of movement the other direction. Take a rod reading.

Subtract your rod readings and calculate the total angle that the telescope tilted from "peg" to "peg". Angle = arctan (R1 – R2)/D.

Submit: Lab write-up in standard form with good discussions of your methods, results and observations.