PPTools has a very simple (but great) add-in for PowerPoint that will save you a lot of trouble when you're designing PowerPoint presentations. On this web page you can download the Thor add-in. It will open as a separate tab on the PowerPoint ribbon.

It has a very simple purpose. Thor's Hammer lets you position any shape added to a slide to a fixed position and size. So if you're repeatedly adding shapes on multiple slides and want them to be the same size and in the same location on all slides, Thor will hammer them down for you.

After adding your first shape with a particular size at a particular location, with the shape selected, on the PPTools tab click Memorize.

When you add a new shape, you can simply select it, and click on the hammer:

. . . and it will be pounded into position.