Drop-in resolution
Ronda 6203.B vs ETA 955.112: do they swap?
Whether the Ronda 6203.B and ETA 955.112 share a case, and what changes if you move between them.
Close in diameter, not a drop-in. The Ronda 6203.B (26.00 mm x 3.30 mm) and ETA 955.112 (25.60 mm x 3.15 mm) are near in size but differ in height, dial feet or layout, so moving between them means a new dial, hands and often a case adjustment.
The Ronda 6203.B is a Swiss quartz caliber with a second time zone display in GMT-style watches. The ETA 955.112 is a common Swiss three-hand quartz caliber, the ETA rival to the Ronda 515.
They differ in diameter (26.00 mm vs 25.60 mm), height (3.30 mm vs 3.15 mm), calendar layout (dual time and date at 3 vs centre seconds, date at 3), winding behaviour. A quartz movement at 26.00 mm x 3.30 mm carrying a dual-time (second time zone) function alongside the date. Its extra 24h train means it needs a matching multi-hand dial and is not a plain three-hand swap.
Matching diameter and height is necessary but not sufficient. A donor is only a true drop-in when the dial-foot positions, hand-hole sizes, stem length and calendar layout also match. Two movements can share a case and still need a new dial, re-broached hands or a cut-to-length stem.