Alignment
The most commonly taught putting stance is one where your body and feet are aligned parallel to the intended line of the putt. Much like your full-swing set-up, it isn't easy to see if your alignment is open or closed relative to your target line after you have addressed the ball. For this reason, it is helpful when you practice using an alignment rod on the ground to help align your stance. So the PASS putting stroke stick acts like an alignment rod on the floor by the shape of the stick itself. If you set up slightly open or closed to the line of your putt, it is common for your stroke to follow your feet, resulting in a putt that is pushed right or pulled left of your line.