Nu Vu NVT model. Look for, How to calibrate oven temperature instructions? . Example. The default setting is 360F but its actually 340F inside the oven.

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Before tampering with the unit’s calibration, I strongly urge you to contact Nu-Vu directly for their specific guidance to address your problem.  http://www.nu-vu.com/New-website/contact.html

 

Here’s a service & repair manual I found on-line for the NVT:  https://www.manualslib.com/manual/1246883/Nu-Vu-Nvt-3-9.html

Page 11 shows calibration instructions.