Suppose you decide not to change the units for birth weight (leaving it in ounces), but instead you would like to change the units of the independent variable, cigs. Instead of measuring smoking in terms of average cigarettes per day, you would like to measure smoking in terms of average number of packs per day. Let packs represent the average number of packs of cigarettes smoked by the mother per day during pregnancy. Instead of rerunning your regression with packs instead of cigs, you know you can calculate the new regression line by hand. Assuming each pack contains 20 cigarettes, the new regression line will be:.