The phrase "cup increments" refers to adding or increasing something gradually or in small amounts, similar to adding cups to a set quantity. Full definition
If the batter appears too thick, add another tablespoon of milk, and if it's not thick enough, add powdered sugar in 1/4 cup increments until you get your desired consistency. (ericasweettooth.com)
If I do it in the microwave I like to do it in maybe 1.5 cup increments at 50 - 55 seconds with a slight damp paper towel over it. (delightfulrepast.com)
For smaller pancakes, I measure using 1/4 cup increments for a total of six pancakes. (dropthesugar.com)