Tiller is the difference in actual distance between the upper limb to the string and lower limb to the string measured from the base of the limbs (where the limb and riser meet) at a 90 degree angle. Single cam models must be measured from a reference line from axle to axle. The main function of tiller is to allow the archer to more easily and comfortably aim during the draw and release of the shot. Most bows will shoot best with an even tiller which means the distance from the string to the limb is the same on top and bottom. Tiller adjustments are made by adjusting either the top or bottom limb weight adjustment bolt. For example, if you have too much tiller on the bottom limb, decrease the weight on the top limb or increase the weight on the bottom. Hoyt recommends that you initially set tiller equal on top and bottom.
Reflex and deflex are terms used to explain the geometry of a riser. A deflex riser bow will have a higher brace height than a reflex riser bow which generally means it is a more forgiving bow. A reflex riser bow has a shorter brace height which usually translates into a higher performance bow and perhaps a bit less forgiving than a deflex riser bow. Reflex/deflex is measured by the position of the throat of the grip in terms of its location from a line drawn from each of the pocket pivot points on the handle. If the throat of the grip is in front of the pivot point line it is considered deflex, if it is behind the pivot point line it is considered reflex.
A method of measurement has been established to provide an industry standard of draw length and eliminate the variances in the original method caused by different thicknesses of bow risers. The ATA Standard Draw Length is arrived at by measuring the "Draw Length to Pivot Point" which is the distance from the string's nock point to a vertical line through the pivot point of the grip, and adding 1 and 3/4 inches. The 1 and 3/4 inches represents the average distance from the far side of the bow to the bow grips pivot point. Manufactures use this ATA Standard Draw Length when they designate the draw length of a bow.
Brace height is the distance between the pivot point of the grip and the string at rest.