Originally Posted by
pineteam
If I’m on radar vector I use distance times 3 or altitude times 3 + 1nm per 10kt to slow down. Works like a charm on A320 family.
I know it should be altitude divided by 3 but it’s close enough.
Otherwise the managed descent on Airbus works very well.
It's not really that it "should be" one or the other. As Check Airman showed above, it's just a different approximation, with the "multiply by 3" one yielding a slightly steeper descent. Put in degrees, "multiply by 3" gives 3.18 degrees, while "divide by 3" gives 2.86. Also I'd consider the factor that it's much easier (at least for me) to multiply by 3 in my head on the fly.