Apparatus and a method for computing and outputting a putting backstroke instruction for a planned putt of a golf ball during recreational play. A computing means includes means for initializing or customizing according to a specific golfer putting on a specific golf green, the golfer putting at least one initializing putt a pre-selected distance on a level area of a green. During recreational play thereafter, in the preferred embodiment of the invention, the golfer, for each segment of a planned putt enters the applicable grade and length. The computing means outputs to the golfer an instruction for the length of the backstroke recommended, i.e., required for the planned putt. Another embodiment of the invention requires the inputting of the length of the planned putt but excludes the inputting of the grade of the green.