We try to get as accurate of a measurement on each item as possible. Sometimes, very tall clocks (either tallcase or wall-mounted) are extremely difficult to measure. Measurements in our listings are close, but are approximations, done with a tape-measure and visual sighting.
The measurement shown is for the longest part of the item, the widest part of the item, and the deepest part of the item.
If we meaured a Vienna Regulator, for example, the width of the clock shown will generally be that at the widest point on either the base section or the crown. The trunk (or midsection) of the clock would be narrower than that dimension. Likewise, the deepest part of the Vienna Regulator would probably be in the crown or base section. The same is true for most hanging, standing, and shelf clocks.