[hm] Fix Derivative not working due to TempAverage getting reset with every measurement
[hm] Fix Derivative not working due to TempAverage getting reset with every measurement

CapnBry/HeaterMeter,dwright134/HeaterMeter,shmick/HeaterMeter,dwright134/HeaterMeter,kdakers80/HeaterMeter,shmick/HeaterMeter,CapnBry/HeaterMeter,shmick/HeaterMeter,dwright134/HeaterMeter,dwright134/HeaterMeter,kdakers80/HeaterMeter,kdakers80/HeaterMeter,shmick/HeaterMeter,dwright134/HeaterMeter,shmick/HeaterMeter,CapnBry/HeaterMeter,CapnBry/HeaterMeter,kdakers80/HeaterMeter,dwright134/HeaterMeter,kdakers80/HeaterMeter,CapnBry/HeaterMeter,shmick/HeaterMeter,CapnBry/HeaterMeter,CapnBry/HeaterMeter,shmick/HeaterMeter,kdakers80/HeaterMeter