I’m a little rusty in Physics 1, but I think this works. When you calendar is suspended draw a virtual (or physical) line from the point of suspension (the clip) directly towards the ground (it has to be perfect, or close). Now re-position the attachment point and repeat the line. The intersection of the two lines is the centre of gravity. Now, detach the calendar, place in on the wall in the desired position and attach the clip so that it is directly above the centre of gravity. Voila?