The transit level is the fundamental tool for a precision start to any new construction project. Because of the erratic nature of the ground, a baseline elevation must be established and referenced throughout the building of any level structure. Just as a building is only as strong as its foundation, the accuracy of all concurrent measurements depends on this plane of reference being precise. The only way to achieve this and avoid compounding errors is to level the instrument in a solid and accurate manner from the tripod upward.
Leveling the Tripod and the Instrument
Choose a solid patch of ground from which you have line of sight to all the corners you wish to establish. The ground must be flat and solid -- pavement or concrete -- or if it is inclined, then it must be soft enough to accept penetration by the tripod's leg spikes for stability.
Unlock the leg extensions and pull the entire upper half of the tripod upward until it is about chin level, allowing the legs to hang loosely on the ground. Lock the back two legs, then separate them in all three directions using the sliding action of the last leg to find level -- either by eye, sighting across the base plate or using the base plate's spirit or "fish-eye" level. Adjust the first leg until you are as close to level as it will get, then lock it. Unlock the one to its right, then perform the same task until the actual center of the spirit level is found.
Reset all four elevation screws at the base of the instrument to about the middle of their range of operation. Attach the instrument to the tripod.
Turn the instrument telescope so the eyepiece is directly over one of the pairs of adjustment screws for the baseplate. Adjust the two baseplate screws underneath simultaneously toward or away from each other until the instrument's horizontal level reads center. Turn the instrument 90 degrees to the right. Repeat the same thing using the two screws now positioned underneath. Turn it 90 degrees more, then fine tune leveling with the first set of two screws.
Establishing a Level Plane of Reference
Drive a wooden stake into each of the four corners of your desired structure's foundation using the hammer. Stand near the highest, most uphill oriented of the stakes and open the elevation rod to at least the height of the transit from the ground. Have an assistant, or "rod man," hold the elevation rod as plumb as possible, either by means of a built-in rod level or by hand-held level accompaniment. Zero the transit for horizontal level, then aim it at the rod. Call out this measurement and have the rod man mark this elevation on the stake. This establishes the reference plane, including the elevation of the instrument up to the horizontal center line of the instrument's telescope lens.
Turn the transit telescope slowly to the right, duplicating Step 1 at each concurrent corner until all four points have a level mark on the stake. Use this as a point of reference for all vertical elevation measurements from this point on.
Set string lines tightly from corner to corner to establish a working plane of reference for the entire perimeter.