RL Difference Calculator
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
100% FreeRuns in your browserBasic
Enter Values
Enter your values and press Calculate to see results.
How to use this calculator
- Enter the known RL and the backsight and foresight staff readings.
- Press Calculate.
- Read the new RL and the height difference.
How it works
New RL = known RL + backsight − foresight; the height of collimation = known RL + backsight. This is the rise-and-fall basis of differential levelling.
Worked example
RL 100.000, BS 1.250, FS 0.880. New RL 100.370 m.
Frequently asked questions
Backsight or foresight first?
Backsight is read on the known point; foresight on the new point. New RL = known + BS − FS.
Related tools
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.