Grain cart scales on a Weigh-Tronix M640 use the custom calibration method (not standard). Most indicators from Central City Scale arrive already calibrated — usually a final adjustment is all you need. Custom calibration corrects the scale by a ratio: you weigh a load, note what the M640 shows, then compare it to what it actually weighed on a certified scale (the elevator).

1. Set the CONFIG number

Under the CONFIG menu, the number is read digit by digit:

  • First two digits: always 98 for grain carts.

  • Third digit — display increment: 3 = 10 lb, 4 = 20 lb, 5 = 50 lb update. Your choice.

  • Fourth digit — printer: set to 9 if you use a printer (harmless to leave in if you don’t).

  • Last digit: always 0.

Common grain cart CONFIG numbers: 98300, 98390, 98400, 98490, 98500, 98590.

2. Pick your starting custom number

CCS grain cart systems are dual-bar systems. Which starting number you use depends on how the system is wired — check the junction box:

  • 3-bar with resistor (junction box has external 5-pin plugs): start at 37500

  • 3-bar, no resistor (wires hard-wired into the junction box): start at 27775

  • 5-bar Weigh-Tronix (never uses a resistor, CONFIG 98590): start at 45000

3. Work out the new custom number

Formula: (actual weight ÷ displayed weight) × last custom number.

Example: certified scale read 58,654 lb (actual); the cart showed 59,240 lb (displayed); current custom is 37,500. 58,654 ÷ 59,240 = 0.9901; 0.9901 × 37,500 = 37,129 = your new custom number.

4. Enter the new calibration

  1. Press and hold Hold/Menu for three beeps — display shows SET.PAS.

  2. Using RM (raises the digit) and Hold/Menu (shifts to the next digit), enter 640, then press Print/Select.

  3. Press Print/Select again — display reads CONFIG. Press Hold/Menu — display reads CUSTOM.

  4. Press Print/Select — the last custom number appears (note it for the formula).

  5. Enter your new custom number with RM and Hold/Menu, then press Print/Select (display reads CUSTOM).

  6. Press G/N to reach 640, then G/N again to return to weighing. Calibration is saved.

Checking it: the best check is to stand on the hitch while the cart is hitched to the tractor — it won’t read accurately on the jack stand. The custom number is a starting point, not a constant; it settles to within about 1% as you dial it in, so a few passes may be worth it.

Questions, or want us to check your calibration? Call Central City Scale at 800-582-3175.