Its lunch time and I continue reading about the temp display. The other conditions vary by year and the ones for the later car are simpler so I will repeat them to continue the answer about testing the reading for accuracy.
"When the ignition is turned on or off and with an engine temp less than 60deg C, the current temp is always stored and displayed.
When the ignition is turned off and with an engine temp less than 60deg C the temperature last measured is stored and displayed.
When the ignition is turned on and when an engine temperature is less than 60(C The stored temperature is displayed."
There are two reasons to write this. One is to show the poor nature of the text that MB techs must decifer. The 60(C is not a misprint on my part. It might lead one to believe that the "less than" sign (< ) which I paraphrased might also be misused in this quite contradictory text.
The second reason is to say that they are pointing out that the actual temp might not be displayed in the interest of not reading the radiator heat after a period of inactivity.
Bosch Master, ASE Master, L1
33 years MB technician