Subdials are the secondary dials recessed into the main dial of a chronograph — or any watch with complications requiring separate indicators. Each subdial has a precise function: small seconds, minute totalizer, hour totalizer. Their position, number, and finishing define both the readability and visual identity of the piece.
The most common configuration is the tricompax: three subdials at 3, 6, and 9 o'clock — or in variants with the third positioned at the bottom, as in the layout that equipped many twentieth-century Swiss chronographs. The bicompax (or two-register) uses only two, typically for chronograph seconds and minutes; the dial gains space and symmetry, but loses a degree of information. The Moonwatch is the most famous bicompax example: one subdial measures running seconds, the other counts hours and minutes on overlapping scales.
The position of subdials relative to the dial plane is never neutral. Patek Philippe on the 5370P sets them slightly lower — a choice that improves contrast between background and indices and makes reading more immediate in raking light. At the bench the difference is obvious: a flat subdial blends into the rest of the dial, a recessed one casts its own shadow.
Finishes vary considerably. Azurage — fine parallel ridges — is classical on black or blue subdials, as on the Carrera Glassbox. Matte finish against a polished background is typical on sporty bicompax models: the Cortina 1956 executes this with precision. Circular brushed rings that delimit the subdial from the outside, as on Christiaan van der Klaauw watches, are instead a way to visually isolate the complication without using color.
Chromatic effects on subdials have their own nomenclature. The traditional panda has a light background with dark subdials; the reverse panda inverts the relationship, dark background with light subdials — the classic scheme of the Daytona 6263. There is also a reverse panda in a more subtle sense, where both materials are identical but tones differ, as happens on certain meteorite dials where the subdials reveal a Widmanstätten pattern different from the background.
Subdials can take unconventional forms. Squared-off circular registers — circular with squared corners — are a hybrid solution that breaks the repetition of round shapes without disrupting the dial's geometry. Sandwich registers, built in overlapping layers, add physical depth beyond the visual: the technique is favored by independents but costs assembly time.
From the bench I'll add something magazines rarely mention: a subdial misaligned by even half a tenth of a millimeter from the dial's axis is visible to the naked eye. It's one of the first checks I perform when examining a piece.