The pinch test involves using calipers to measure skinfolds at certain points of the body. Once the pinches of skin results are taken they are entered in to a formula which enables you to calculate an overall body fat percentage.
The places on the body where measurements are taken have been picked as they reflect the percentage of overall body fat. This is a simple way to test body fat however it does rely on the individual testing maintaining a good degree of accuracy when testing. If the person testing does not have the right level of skill the results can be very inaccurate.