Why is the measured mains voltage does not match the mains voltage readings according to the HMI on ATV61 or ATV71?

Issue:
Why is the measured mains voltage does not match the mains voltage readings according to the HMI on ATV61 or ATV71?

Product line:  
Altivar ATV61 and ATV71

Environment: 
All models, all serial numbers

Cause:
Flat topping on the input AC waveform. 

Resolution:  
The HMI's mains votage reading is a measurement of the DC bus  not a measurement of L1 L2 L3.   Calculate the Mains voltage by taking the DC bus value and divided it by the square root of 2.