I use a " x " paper chess board that I cut out from a score sheet. I'll look at the paper and move an imaginary knight around the board, for example: find Nf5 [Ng1-Nf3-Nh4-Nf5], find Nf6 [Ng1-Nf3-Nh2-Ng4-Nf6] or practice openings, checkmates, tactics...everything and anything.‼️ . . . . . . I find it much easier to calculate variations without pieces on the board. While playing internet chess, it's difficult for me to imagine my White dark square bishop capturing Black's knight on f6, look at the board, and NOT see that knight anymore, because it is STILL there. Well, it's not completely that bad, but it ‼️