You learn the specific formula for summoning Watchers as part of the training in all Planar Summons Spells, thus no matter which version your character knows s/he also knows how to summon watchers
The summons brings forth a small spiritual watcher of
Attributes: ST 1 [-90], DX 8 [-40], IQ 9 [-20], HT 7 [-30]
Secondary Characteristics: Size = SM -1, Enhanced Speed +1 [+20] Speed 4.75, Move 4, Dodge 7. Perception +3 (12) [+15]
Advantages: Flight (Lighter Than Air -10%) [+35], Immunity to Metabolic Hazards [+30], Injury Tolerance (Diffuse) [+100]
that will be under the complete control of the Summoner ( Though abuse of Watcher spirits can cause some weird effects). The Watcher is an Astral creature, though it can manifest on the material plane for brief periods. When active on the Material Plane a Watcher can be used to ground a Spell, but this is considered to be Excessive abuse and can lead to repercussions.