A golf putting aid is used with a putter having a handle, a putter head, and an elongated putter shaft. The putting aid includes an elongated member affixed to the putting aid and an attachment member capable of detachably securing the putting aid to the shaft of a putter.The method comprises attaching the putting aid to the shaft of the putter and using a level on the putting aid to determine the slope of a green between two points on the surface of the green. The putting aid may be used either with, or without the putter.