Traditionally with a wire and a spirit level, in fact the wire and the spirit level are two very different measurements, they measure different characteristics of a guide. Here the wire measurements are absolute measurements where the spirit level measurements are incremental. Additional we measure an angle with the spirit levels and calculate the hight. So there can be large differences between spirit level measurements and laser based or granite stone based measurements.
The advantage of our ProLine system is here that we measure both axis simultaneously and absolute!