Voltage Regulator
This is where my amp gauge is after it's been running for a minute or so
That's about right.
One can estimate a little better after observing where the needle sits with everything off.
But IMO the main utility of the built in ammeter is to observe the behaviour, so seeing approximately 5 to 10 amps charging after a minute is OK.
but at first start it is just below +40...
I have seen similar and suspect this happens when:
A battery is losing its storage capacity.
Slight delay in the voltage regulator's initial response to full fielding after start up. I *think* this is worse with high draw alternators (such as revised squarebacks).
The voltage response can be observed by connecting a voltmeter during start up.
Bonus from doing this is you can observe the voltage drop when the starter is engaged. If its down around 9.5 - 10 Volts when the starter is turning its an indicator the battery capacity is on the low side although still functional.
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edit: Dana in post 2 is describing similar observations.
This is a situation where using a portable voltmeter in conjunction with the built in ammeter can reveal a lot more than either alone.