Sorry about posting lots of topic at once, but I finally just bought simulator and this product and there's info that can't be found yet by searching.

By searching some forums, I could gather a little info about realism settings and there's a recommended setting in the introductory manual.

But the option "Enable gyro drift" is somewhat unclear and the manual also doesn't say about it.

I know about basic theory about it and this product is also affected by this(it looks like to me). But I'm not sure about whether I check this option.

There are some mentions in web but they are all different opinions.

The Intro manual doesn't mention it because it is irrelevant. That setting will be used by an aircraft that uses the default heading gyro gauge, the PMDG 777 does not use any default gauges that I am aware of; additionally, all modern transport aircraft have slaved gyro systems, even the DC6, where the gyro drift due to precession is mitigated.  I believe this setting applies only to small GA aircraft, and many of them have slaved gyros now.

sometimes weird behaviors remain in the sim though. i turn off gyro precession when flying jets because frankly it's not necessary.

but for example, i have found that in FSX there is a general aviation fuel pump in EVERY aircraft that can be turned on if you have a saitek switch panel. even if you've deleted all the key mappings for fuel pumps, flick the switch and the little cessna fuel pump noise comes on. who knows what is going on there, but you can do it even while flying a PMDG jet. have not tried with p3d. who knows why there is a GenAv fuel pump in there.

i'd leave it turned off and only turn it on if you're flying an aircraft like the constellation or b377 or some GA aircraft. but even then, looking at the mag compass in the sim is a lot harder than it is in real life - it's quite difficult to read the numbers accurately in the sim so i tend to just use the "D" key or leave precession off completely.