This weakaura shows you how many healing spheres you have out and what is the expected healing (without crits) what you'll get by using Expel Harm. The formulae are the following:
Basic expel harm without orbs: extra healing power*1.2*(1+versatility/100) - verified by Blizzard
Healing for one orb: extra healing power*1.563*(1+versatility/100) - Blizzard states that an orb heals you for 150% of spell power (hence the multiplier should be 1.5), however in reality it is 156.3% of spell power. I don't know if it is a bug, will update if this gets changed.
So the formula for X orbs is: basicHealing + X*orbHealing
Tested, works. Tell me if there are anything wrong with it.