Some, not all, are helpful. These different ways can sometimes help in changing the units used for the expression of a quantity. A few slope or velocity based examples follow. Note that care must be taken in selecting the ratio of units whose value is 1. A faulty choice will introduce more units instead of permitting some to cancel.
Substitution replaces one unit by an expression for it in terms of another.
With this method, there is little or no hazard of introducing units that don't cancel, but the algebra or arithmetic requires a little more thought. The choice of unit conversion method depends on where you would like to do the work or reasoning. 1 Introduction 2. Ski Trails 3 Sign Analysis 4. More Analysis 5.