This is just a simple slide in holder that was made in TinkerCad for my old Sharp EL-344G solar calculator. Yes, I am that old. This holder has a slot in the back so it's easy to pop it out with a finger. This keeps it off the surface of my desk which seems to always be a mess. I know that most use the calc on the phone or on the laptop but old habits die hard. 

I used Prusa Slicer and added internal supports with these settings, Support On Build Plate Only, Support type "Snug" " Top Contact Z Distance (Detachable 0.02)", "Top Interface Layers (1 Light) Interface Pattern "Concentric" These settings should make the supports easy to remove and not leave anything behind. Keep speeds under 850mm/sec for best results used PLA+ Filament from ELGOO with a 225C print head temp and a 65C bed temp.