I like this analysis a lot! But there's one more twist to the story: are
we even using the right definition of year? There's actually several
different ways we can define a year:

NIST-811 defines the light-year "year" as 365.2500 days and the
"common year" as 365 days exactly.

The sidereal year: the time it takes for the stars to return to a
fixed point. That's 365.2563 days.

The tropical year: the time between vernal equinoxes. That's 365.2421
days.

The anomalistic year: the time between points where the earth is
closest to the sun. That's 365.2596 days.

For each of these we can define the microcentury as a hundred
microyears. So the sidereal microcentury is +35.81 seconds, while the
tropical microcentury is +35.69 seconds. The NIST microcentury is +33.6
seconds, while the Julian microcentury is +35.76 seconds (as you
calculated).

Personally, I'd define a calendar microcentury as a four-millionth of
400 years to match the leap year cycle. That'd give us +35.692 seconds.

## Hillel Wayne said:

I like this analysis a lot! But there's one more twist to the story: are we even using the right definition of year? There's actually several different ways we can define a year:

For each of these we can define the microcentury as a hundred microyears. So the sidereal microcentury is +35.81 seconds, while the tropical microcentury is +35.69 seconds. The NIST microcentury is +33.6 seconds, while the Julian microcentury is +35.76 seconds (as you calculated).

Personally, I'd define a calendar microcentury as a four-millionth of 400 years to match the leap year cycle. That'd give us +35.692 seconds.