When I am using my PicoCalc it is always sliding around on hard surfaces. Initially, I got some silicone cupboard bumpers, which were clear and stuck them on the back shell. This made the calculator rather thick for one of my pouches, and I noticed the small feet included in the design.
So I pulled the large larger silicone bumpers off, found a sheet of neoprene sticky back, and use a leather hole punch to create the correct diameter feet, which I inserted into the sculpted feet on the back shelf.
Now it doesn’t slide around! I initially bought the neoprene sticky back to create replacement fee for my Hewlett-Packard restorations. It came in handy with the PicoCalc!