Deviation, measured in degrees, is the difference between the calculated initial direction of the putt and the actual direction of the putter at impact. This measurement can help to visualize the error margins and identify areas of improvement in the putting stroke. A small deviation can indicate a consistent and accurate putting stroke, while a larger deviation can indicate that the putter is not being aimed correctly or that the stroke is not consistent. By identifying the deviation, golfers can make adjustments to their technique or equipment to improve the accuracy of their putts.