One Bad Subtraction
A stamp with one bad subtraction is characterized by a significant positive peak and a significant negative peak. The most obvious cases will have two opposite peaks of about equal size, but as long as they are both significant compared to the rest of the field, it counts as a bad subtraction.Many Bad Subtractions
The easiest description of a stamp with many bad subtractions is a mess of peaks and troughs. If there are many significant positive and negative peaks and they seem to be scattered all over the stamp, it is likely a stamp with many bad subtractions.Streak Of Bad Subtractions
A stamps with a streak of bad subtractions contains a line (not necessarily horizontal or vertical) with positive and negative significant peaks.Transient
Finally, the purpose of this project: to find transients. At first sight, you might already notice a striking difference between a stamp containing a clean transient and one with bad subtractions. Stamps with a transient contain one large positive or negative peak. Ideally, the rest of the stamp would be flat, but as long as there is only one prominent peak, the stamp can still be labelled a transient.