Calibrating EGT gauge

[ArrowFlyer86]

Each time I fly and lean the mixture I use my EGT gauge to track the highest EGT achieved with the yellow needle, then I add mixture until it comes down by 2-3 notches (50-75F).

Here's my dial model for reference:


I've never used the asterisk (*) marker that is 80% of the way up the dial as a reference point.

But while googling it's purpose I found this:


Questions:
(1) If I were to calibrate, do these gauges usually hold their calibration well? Or is it something you have to do frequently?
(2) If calibrated, the asterisk point would only be valid "Peak EGT" for that altitude/power setting I calibrated it to. If I were to change my cruise by 2-3k feet or a different power setting, then I assume I'd do my normal leaning process ignoring that asterisk?
(3) For those with these simple EGT gauges, do you make use of the calibration or just manually lean as I specified above? Note: I don't have an engine monitor, just oil temps and EGT gauge.

 

[Salty]

Why would you calibrate an instrument that's meant to only show differences? Each tick is 25 degrees. That's its purpose. Otherwise it would have numbers on the scale.

 

[ArrowFlyer86]

Why would you calibrate an instrument that's meant to only show differences? Each tick is 25 degrees. That's its purpose. Otherwise it would have numbers on the scale.

Great question, and no disagreement here.
But also... Alcor puts it on there for a reason, so I imagine some people must be using it?
IDK - I've never calibrated it and only ever used it as a relative tool, but I'm curious if others get any use out of calibrating.