Magnetic compass

You'll need a 20x10x2 mm square magnet. Use slot in the compass to put the magnet in. 

You can add a bit of glue, but check the polarity before - if magnet is reversed, then North points to South. Then just turn the magnet around. 

Magnet works on water or when hanged from a thread. 

For multi-color print, make color change at 1.5mm. 

I've included a print file for MK3S with color change (at 29 min). 

Printed with 0.15 layer height, no supports.