Originally Posted by Prism99

The Rule Steady and Slidelock are different rulers.

The Rule Steady is indeed designed to be placed on top of rulers; it has two uneven sides, one of which is higher to compensate for the height of the ruler. The Rule Steady has rubber grips under the two sides. Here is a link to a Youtube demo of the Rule Steady:
https://www.youtube.com/watch?v=ZKpqNqK1q80

The Slidelock does not have two uneven sides and was not designed to be used on top of rulers; it is designed to be used as a cutting ruler itself. It has a single row of round "grippers" underneath the handle. The ruler itself has holes in the ruler under the handle. When the handle is pressed, the grippers go through the holes in the ruler to "grip" the fabric. It will not work on top of rulers in the same way that the Rule Steady does; the design is different. Here is a link to a Youtube demo of the Slidelock:
https://www.youtube.com/watch?v=x1hyEDLC4S8