If you find that 0.125" shims are needed under one end of a 4' long base plate using a 1' level, how much should be added under the base plate to level it?

When levelling a system, you need to consider the total length of the base plate and the distance from the level point to the point where the shims are placed. In this scenario, the 4-foot long base plate is being levelled with a 1-foot level.

If you've determined that 0.125 inches of shims are required at one end of a 4-foot base plate, you need to account for the ratio of the length of the level to the total length of the base plate. Since the base plate is four times longer than the level, the amount of shim needed to ensure proper levelling is also scaled accordingly.

Thus, if the required shim under a 1-foot section is 0.125 inches, to maintain that level over the entire 4-foot base plate, you would multiply the shims needed (0.125 inches) by the 4-foot length of the base plate. This results in needing to add 0.5 inches of shim beneath the base plate to properly level it.

This principle relies on understanding that a change in elevation over a greater distance requires a proportional increase in the amount of shim being used.