Rectangular

Rectangular cases are quoted as width by length, for example 25 by 34 millimeters. The long axis runs up the forearm rather than across it. The tank format that defines the shape dates from 1917, when the case sides were drawn to echo the tracks of a tank. Its proportions have barely moved since because they work on almost every wrist.

Thickness is the practical advantage. A rectangular case usually houses a small quartz movement or a shaped mechanical movement, and both are flat. The watch often measures 6 to 8 millimeters top to bottom, so it slides under a shirt cuff where a sports watch jams. Shaped mechanical movements are rarer and more expensive to build, which is why most affordable rectangular watches run quartz.

Limits come with the format. Water resistance is usually 30 meters, 3 ATM, meaning splash protection only. The dial is narrow, so complications beyond a small seconds or a date rarely fit. Crystals are custom shapes, and if one breaks on an older model the part may no longer exist. For a watch that lives under a cuff at a desk, none of that matters much.

Beside a square case, a rectangle covers less wrist for the same overall length, because the width stays narrow. A 25 by 34 millimeter watch sits comfortably on a 145 millimeter wrist where a 34 millimeter square would overhang. Check the strap attachment before you commit. Lug widths of 16 to 18 millimeters are normal here, and some models use fixed bars you cannot change at home. Leather is what wears out first on this shape. The case is light, so the band does all the work of holding it flat against a moving wrist.