If the Keeper is the "head" then the Monitor is the "feet" to ground the circle. The Monitor is a part of the circle but still separate, they watch and maintain the life signs of those in the circle. By resonating to anothers magnetic field and being in close rapport it is possible a Monitor can touch anothers starstone/matrix without harm.
Through the observance of the "energy currents" of a body the Monitor can regulate the energies of themselves and others keeping them safe from injury or total exhaustion. Their job can include controlling blood flow (headaches, strokes), relieving muscle tension, restarting a heart and helping a body remember to breath, as well as other biological problems.
Monitors wear white robes, even those with little laran can monitor, that is why when students are trained at Towers being a monitor is one of the first skills they learn. The best Monitors appear to be those with the Ridenow Donas or have a strong level of empathy .
The Monitors oath is also the first oath students take in the Tower. The oath binds you only to the basic principles that you swear never to use your starstone to force the will or conscience of any living thing, never to invade the mind of any other unwilling and to use your powers only for helping or healing, and never to make war.