Patterned risers are very useful - not that anyone would gauge off them of course. Or perhaps a manufacturers decal such as a dirty great big manufacturer logo right on a compound riser cutout. I'm not bitter.
I seem to recal EFAA have a rule which says pattern must be taped over but you get the point there's generally a reference point to get you in the ballpark.
Learn your favourite distance such as 20yrds and get it instinctual so as you always draw to it - mine is 10yrds. Then it's a case of going up in increments - i always found this easier than trying to gap off the target. Mostly practice if I'm honest, whatever works.
I have now found something in the IFAA/EFAA rules that helps.
It is in their list of definition of terms:
'Sight- Any device attached to or incorporated in the bow or attached to the archer's body, other than normal reading glasses, markings or blemishes on the bow limbs and/or bow riser, other than caused by normal wear and tear, which in the opinion of the IFAA Technical Committee may assist the Archer in aiming the bow.'
So you can't use any object as a sight.
But fingers are okay? Presumably?
Anyway, this weeks practice I tried gapping using the target face only. So you knock an arrow and then use the point to count up or down faces, choose a suitable mark and then take the shot. e.g. my 25 yards is 3 faces low; my 65 yards is 2 faces high.
This works for me and I intend to persevere with it, assuming nobody tells me my arrow point is then a sight (!)