If you bought the gauges from genos they can take care of you. From what I understand, the gauge is calibrated based on the resistance of the wire and thermocouple and how much that resistance changes. By going to a longer or shorter cable than calibrated for you can throw off the gauge (if I understand this correctly). Genos, sells their gauges with several different cable lengths and each gauge is callibrated prior to shipping (from what they told me, and I believe them). So. . . . if you order the gauge from genos with the right length cable, you should be good. If you take a gauge that came with a 6 foot lead and attach it toa 15 foot lead, i think you may possibly be off. Don't have a clue how much, though. Good luck!