17% of 10 degrees (if that's what it is) is 1.7 degrees.
How long can you fly a heading of 11.7 degrees for?
On a plane with a non-slaved DI that drifts a few degrees every few minutes?
With a bit of turbulence which chucks the compass around by plus or minus 10 degrees, so you can't read it properly and thus you can't adjust the DI from it.
This is about rules of thumb. Usually, all you have is the surface wind when you departed, say it's 270/10. You are at 3000ft, and a quick stab gives you 290/30. You have to fly a leg, or enter a holding pattern on which the fix is on a northerly track, which means you will have just about all of that 30kt as crosswind.
15 degree offset on the heading.
If you want more accuracy, you get yourself an air data computer, or you very carefully read the speedo, the DI, the OAT, the altitude, and work it all out. But then, with all that kit, you won't be asking these questions in the first place
I have never used a playstation.
If you are ex RAF (I suspect you are) they would have taught you to do things more precisely. But then you would have been selected from the cream of the cream, at the age of about 18, and put into an intensive training regime where you don't have to worry about job, life, wife, ex wife, kids, etc. This is a far cry from today's PPL intake. Fortunately you didn't have to fight too many wars; the other side won't be doing dead reckoning if they've got something better. I had exactly this discussion recently with a serving RAF instructor; he tried hard to justify dead reckoning but really couldn't explain how they could perform in any real action.