This video is useful for Trades Math, where students are learning about how to do math calculations where a certain grade (or slope) is needed. Plumbers, for example, need to know about this! Note: Length is generally a horizontal distance, but sometimes length will be referred to the length of a pipe (that is going to be on a slope). The grade is so tiny (often 2%) you won't need to worry about this issue! Just treat length as length, no matter what!