RosettaCodeData/Task/Greatest-common-divisor/Sinclair-ZX81-BASIC/greatest-common-divisor.basic

 10 LET M=119
 20 LET N=544
 30 LET R=M-N*INT (M/N)
 40 IF R=0 THEN GOTO 80
 50 LET M=N
 60 LET N=R
 70 GOTO 30
 80 PRINT N