It doesn't matter it's a stable reference to compare the fork and A440. If it's so out of tune that the beats are too fast or slow to hear well, rough tune it close enough so you can hear the beats.
Tuning to the fork by just matching the pitch as you listen to the fork will get you close, but it's hard to get it right on. We are shooting for a pitch that is within one cent of the fork margin of error, to get that close, I have to use a beat check to make sure I'm right on. So yes, faster and easier, but not as accurate as comparing the beats.
Very useful lesson! But what if the F2 is out of tune?
It doesn't matter it's a stable reference to compare the fork and A440. If it's so out of tune that the beats are too fast or slow to hear well, rough tune it close enough so you can hear the beats.
Can't you just tune A4 to the fork? Seems faster and easier, so what is it I'm not understanding?
Tuning to the fork by just matching the pitch as you listen to the fork will get you close, but it's hard to get it right on. We are shooting for a pitch that is within one cent of the fork margin of error, to get that close, I have to use a beat check to make sure I'm right on. So yes, faster and easier, but not as accurate as comparing the beats.
Why not just carry your tuning fork in your pocket? That way, it's always the same.