Explanation

Rise or fall is the difference in elevation between two points in a survey. In your case, if the backsight reading taken on a benchmark (B.M) is 2.045 meters and the foresight reading on a point is 2.68 meters, the rise or fall is:

Rise/Fall = Foresight Reading - Backsight Reading

Rise/Fall = 2.68m - 2.045m

Rise/Fall = 0.635m

So, in this case the foresight point is 0.635m higher than the B.M