This was posted in the official rulings thread on the PP forums a couple days ago. Just FYI.
Control Area
There seems to have been some confusion lately about the measurement of warcaster control areas. The rule actually seems to be deceptively simple. A warcaster is powerfully sensitive to his surrounding making him virtually omniscient within his control area.
A player may measure his warcaster's control area at any time. While measuring his control range, a player may determine the proximity of other models to his warcaster. Specifically, a player may measure the distance from his warcaster to any other model within the warcasters control area, at any time. He is not limited to only determine if a model is within his control range or not. The rule is open ended because a player may make the measurement at any time for any reason. However, this does not mean a player can measure the distance between any two models within the control area at any time.
Originally, the intent of the game was not to allow any premeasuring. However, some spells, like Fog of War, make it virtually impossible not to do this frequently, thus it is necessary to allow such measuring at all times.
Keep in mind, if you make a measurement the information must be shared with your opponent as well... So he will know how close you are as well. Experienced players will keep in mind that overly using this ability may telegraph your intentions to your opponent.
It has come to our attention that we left out some errata on Reinholdt's Spyglass that we intended to get out there over a year ago... What can we say, he's short and we overlooked him. Spyglass should read, "Warcaster may measure the distance between himself and one other model within line of sight." Just to clarify, that means if you are playing on an 8' table Reinholdt may be used to used to measure the distance to a model 8' away. <!--IBF.ATTACHMENT_1120595-->