Often, it is necessary to know the slope of a hillside. If we were going to build a road up a hill, we would need to know the degree of slope so as to determine whether the road could go straight up the hill or not. There are limits to the ability of vehicles to climb hills, and safety factors regarding vehicles driving down the hills. For example,
heavy trucks sometimes lose their brakes on steep downgrades. This can be extremely dangerous. Rather than build a road up a hill and watch to see how many people are killed on it, the engineers measure the slope and compare it to their statistics which show vehicle specifications and safety limits.

Structural engineers also have statistics which indicate the limits of slope on which it is safe to erect buildings.

A clinometer (say "kly-NOM-mitter") is an instrument used to measure the slope of a hillside. A clinometer can be made by mounting a plastic protractor or a protractor drawn on an index card on a wooden ruler or stick. An indicator line made from a thread and weight (such as a paper clip) can be suspended by a thumbtack from the center of the protractor's diameter.

When the instrument is tipped up, the number of degrees from the horizontal can be read on the protractor. (A soda straw attached to the top of the ruler aids in the sighting of an object at the top of a hill.)

The angle indicated on the protractor gives the slope of the hill.

What other factors have to be determined before any kind of construction can be done on a hillside?