100 REM RELFILE RECORD-LENGTH FINDER IN 8 TRIES
110 REM ELIZABETH DEAL AND HOWARD HARRISON
120 REM    INDEPENDENT OF COMPUTER AND DISK ROMS
130 REM    INDEPENDENT OF RELFILE FORMAT (REG OR JUMBO)
140 REM    DOES NOT SCAN ANY DIRECTORY BYTES
150 REM    IS A READ-ONLY ROUTINE - USES JUST CHANNEL 15
160 OPEN 15,8,15: OPEN 1,8,3,"RELFILE,R"
170 MN=1: MX=254         :REM RECORD SIZE RANGE
180 IF MN>MX THEN CLOSE 1: CLOSE 15: PRINT"LENGTH=";MN-1: END
190 SZ=INT((MN+MX)/2)    :REM TRY LENGTH SZ=MIDPOINT
200 PRINT#15,"P"CHR$(3+96)CHR$(1)CHR$(0)CHR$(SZ):REM REC#1, POS SZ
210 INPUT#15,E,E$,E2$,E3$: REM DRIVE KNOWS ALL ABOUT LENGTH!
220 IF E=0  THEN MN=SZ+1 : REM VALID LENGTH, TRY HIGHER
230 IF E=51 THEN MX=SZ-1 : REM BAD LENGTH, TRY LOWER
240 IF E=0 OR E=51 GOTO 180
250 PRINT"BAD DISK ERROR-"E;E$,E2$,E3$