MK4 Heated Bed LCD Temperature Mesurements Seem to be Incorrect.  

MK4 Heated Bed LCD Temperature Mesurements Seem to be Incorrect.

I had some warping of corners on parts which were "close" to the outer edges of the heated bed, but when I printed the parts directly in the center of the heated bed, warping did not happen.   I made sure the heated bed and the textured sheet was perfectly clean. I was using PETG, starting the first layer at 85C then dropping back to  65C for the remaining layers.  So I sampled various heatbed temperature settings using a small point thermocouple probe on my Fluke 17B+ multimeter to make the measurements:

I chose to sample around the middle of the bed and the front right of the bed ( yellow X's):

I made measurements from 65C to 100C, dialed in on the MK4 LCD panel. My results:

-------------------------------------------

MK4          Center         Right Front

LCD            Probe             Probe

Setting     Reading        Reading

--------      ------------     ----------

65C            54C               53C

70C            56C               58C

75C            60C               63C

80C            64C               68C

85C            68C               72C

90C            72C               77C

95C            76C               82C

100C          80C               86C

---------------------------------------

It appears the LCD heatbed temperature does not match my probed temperature by quite a bit.

I confirmed the accuracy of my probes by screwing the V6 nozzle temperature probe (blue box) into the hot end instead of a nozzle, while simultaneously pressing the Fluke probe onto the hot end. The MK4 LCD and my probes all measured almost the exact same temperatures across a range of MK4 Nozzle heat temp settings.

The heat bed and heat bed thermistor (installed at factory) are brand new from Prusa and had never been used.

I wish there was a way in the LCD settings panel to add "offsets" to apply to the heatbed temperature to bring it more in-line with the correct temperature. Without this a guess I will have to skew my temp settings in the slicer, specific to my MK4?