Positional Error and Adjusting to Positions

Positional error is the variation in a watch's rate that arises purely from changing its orientation relative to gravity, and it exists because a balance wheel is a real object with mass, resting in real pivots with measurable friction, rather than an idealised frictionless oscillator. Lying dial-up or dial-down, the balance staff's pivots bear evenly on their end stones under gravity; turned onto an edge, the pivots instead bear against the sides of their jewel holes, changing the friction the balance experiences through its swing and, more subtly, revealing any residual poising error in the balance wheel itself as gravity now pulls unevenly on its rim.

The conventional testing regime evaluates rate and amplitude in six positions: dial up and dial down (the two 'flat' positions, representing a watch left on a table or in a drawer), and four vertical positions corresponding to a wristwatch's crown pointing up, down, left and right, chosen because they correspond to how a worn watch is actually oriented through a day and night — crown up and crown down being the two most common positions for a watch left on its side overnight or carried in a pocket.

Adjusting a movement to positions means physically correcting the sources of positional error revealed by this testing: poising the balance wheel so its centre of mass coincides exactly with its axis of rotation (removing the tendency for gravity to make one side of the rim consistently 'heavy' in a vertical position), ensuring pivots and jewel holes are round, smooth and correctly sized, and, in the highest grades, further shaping the hairspring's terminal curve to compensate for any remaining position-dependent variation the mechanical adjustments cannot fully remove.

Historical marks such as 'Adjusted to 5 Positions' or 'Adjusted to Temperature and 5 Positions', found on higher-grade American and Swiss pocket watches especially, indicate that a movement received this positional adjustment as a distinct, additional stage of finishing beyond ordinary assembly, and genuinely correlate with tighter positional rate tolerances in period grading systems — but the phrase appears on movements of real, verifiable variation in quality, and a collector should treat it as one data point supporting attribution and grading rather than as a guarantee of a specific numerical performance, particularly on a movement whose adjustment may have degraded through a century or more of wear, prior servicing, or magnetism.

For a currently running watch, positional testing and re-adjustment is specialist work carried out on a timing machine by a trained watchmaker, since correcting a poising or pivot fault means removing and working on the balance assembly itself; a home reader's useful takeaway is the ability to understand and sensibly discount marketing language built on positional adjustment claims, covered further in the lesson on reading auction and dealer descriptions.