iPad / tablet mount for Concept2 rower

During the first lockdown, I tried to buy a tablet holder for my Concept2 rowing machine to watch video during my workout, but all options were sold out. I printed out the [Tablet holder with 4 tension claws](https://www.thingiverse.com/thing:3283103), but placing and removing the tablet is uncomfortable with 4 moving arms.

This design is a full redesign that fits the same screw holes as the design references above, but has two fixed arms and one sliding one, making the handling of the tablet much easier. The size fits my Android tablet, but can be adjusted to fit an iPad as well.

The best printing result is obtained by adding supports only for the recess with the four screw holes and leaving the slits for the arms free. The arms fit very tightly, so you might need to remove some of the material from the overhangs after printing with a hobby knife.