My spa is a 2002 Regency Spas, made by National Equipment Mfg. Corp.
The circuitboard system has no mfr. name anywhere. There are both a
knob thermostat control on the box at the heater and a topside
pushbutton control at tubside. The heater is electric Vulcan style
(flow-through 2" stainless tube). Pump is 220v and heater is 110v.

The spa heats normally, but quits short of target because the topside
digital thermometer reads 5 degrees warmer than actual water temp. Is
there a way to calibrate the digital system to get the reading in sync
with the actual water temperature?