By 1988, compounds were remarkably uniform, surprisingly like the original Allen patent drawing. many having cams; but there were two problems: the wheels or cams were narrower in order to try and minimise the recurring problem of bow limb torque; narrower wheels brought the string (and, hence, the arrow) closer to the cables near the centre line of the bow: inevitably, the arrow collided with the cables. One or two manufactures widened the wheels; all others added a "cable guard", an angled bar extending from the back of the handle riser to beyond the cables, nudging the cables off centre, out of the arrow path. This ugly addition now disfigures almost every compound bow on the market. But, as we shall see later, there is one notable exception.
For compound bows with a cam or eccentric wheel at each limb-tip (the majority of models) careful adjustments have to be made to the cable lengths and the bolt at the base of the bow limb which adjusts the tension in the limb. Spanners, pliers, screwdrivers are used: the bow must be Tuned, so that both bow-limb tips move in precisely the same path as the bow is drawn and loosed. Much fuss, effort and hard work has been expended in the past twenty-five years in efforts to iron out this problem.
For the Romans, faced with the same problem two thousand and twenty-five years ago when the bow limbs of their arrow-shooting catapults needed to be synchronised, the solution was simple: Vitruvius, writing in twenty-five B.C., stated that the competent artilleryman in charge should have an ear for music. (Presumably he adjusted the tension in each spring, tapping either side with the lever till the musical note emitted was at exactly the same pitch.) Now, that WAS tuning !