Hi, the ZX81 BASIC code is basically near enough the same as the ZX Spectrum version, with a few little tweaks here and there, I'm also using a 16K ram pack so boasting the standard 1K. I try to avoid constant screen printing, limit subroutines, and any unnecessary screen collision checks, keeping the main game loop as optimised as possible. The programming process of this particular game is available on my YouTube channel as it was created during a 5 hour live programming stream, link available on the game page.