I added some things to FloridaMan's awesome Helix Cube.
- Make them stackable with a connector piece (included in files)
- Added tolerance tests in form of thin circles on top and bottom (0.1/0.2/0.3mm bottom, 0.5mm top)
- Added a layer adhesion test in form of a spike in the hexagonal hole
- Added an easily inspectable briding area on the underside
- Made one side mostly flat for labeling and to measure cleanliness of flat walls
- The first layer is in my experience more difficult now compared to before
