Here is a simple but useful way to calculate the horizontal distance between two points.
You take two readings, an upper reading and a bottom reading. The difference between these two readings is then multiplied by a constant.
What is the constant? The constant depends on the leveling instrument used. You can find the constant in the instruction manual for your leveling machine.
The result of this formula will be the distance between the two points.
By viewing this video one can easily learn the technique and calculation.
Please watch the video to learn the method.