Booking and computing
Once the observations are complete and before the back staff and the instrument leapfrog forward the following reductions and quality checks are made. Examples from the fourth line of the observations are shown.
(1) Compute the Right minus Left readings for the back staff and the forward staff. Because these are constants of the invar strips they should be the same. Check that they are within 0.00070mof each other
Back R − L = 4.58562 − 1.42299 = 3.16263
Forward R − L = 4.62135 − 1.45819 = 3.16316
Check 0.0007 > (3.16263 − 3.16316 = −0.00053) > −0.0007.It is.
(2) Check that the forward and back distances are both less than 50 m and that they agree to within 0.3 m of each other.
Distances are 30.1 and 30.2.
3) Compute the Running Difference Distance as the forward − back distance the previous value. And make sure that it stays close to 0.0 m by adjusting future forward or back distances as appropriate.
30.2 − 30.1 0.0 = 0.1
(4) Compute the Right plus Left readings for the back staff. This is equivalent to twice a back staff reading plus a large but constant offset. Do likewise for the forward staff readings.
Back R L = 4.58562 1.42299 = 6.00861
Forward R L = 4.62135 1.45819 = 6.07954
(5) Compute the Running Difference Height as sum of its previous value 12 (Forward R L) − 12 (Back R L).
Running Difference Height = −4.08499 12 6.07954 − 12 6.00861 = −4.12046