oh i didn`t mean to imply that i was always betting 3 numbers, it all depends. If my analyse shows the highest standard deviation and best return on a 5 or 7 number sector, thats what i go for. On the other hand, if the layout has no racetrack and the dealers don`t offer to place the bets for me, i bet 3 numbers or if 5 or 7, then as many as i can get away with before the dealer whack my fingers or gets annoyed with me. Usually that cuts the placed numbers down to 3 - 4 numbers.
The hit rate on a 3 number bet, divertes a lot. Its best suited for a long term play where your intention is to play 75 - 100 or even more spins after your tracking. Otherwise you might fall out between bad scatter streaks, but if you play 100 spins or more and have the bets in the correct place, the edge will usually show sooner or later. 50 - 100 unit bankroll can easyli be the standard to cover bad scatter, depending on the diffyculty of the wheel.
If the intention is to only play 30 - 40 spins, 7 - 9 numbers are better. Or at least 5 numbers. That way you will cover many of the bad scatters too, and you can leave after say, 8 - 10 hits playing a 9 number sector. Or whenever you hit +100 units, whatever comes first.