A hand is equivalent to four inches, what was believed to be the average width of the male hand in Ancient Egypt. This unit is used today to measure the height of a horse (from level ground to the top of the horse's withers).
If a horse is 15.1 hands, the horse would be 61 inches, or 5 foot, one inch. The decimal, when measuring in hands, is not equivalent to the fraction of the hand, but a measure in whole inches. 14.1hh would be 14 hands, 1 inch. 14.2hh would be 14 hands, 2 inches.