Possibly the most visually striking variation, and of course one of the most collectible, is represented by the present example with tropical chapter rings. Tropical dials are the result of a "stealth" production defect, namely the paint does not properly resist to the action of UV light and oxygen and changes color. Given the dramatic looks tropicalization imparts to timepieces, such a defect has come to be a sough-after particularity of the models. While in previous references tropicalization does not occur within a very specific time range, in the case of reference 16520 it appears that only batches of paint made during a certain time can present tropicalization, namely the ones used for timepieces produced between 1993 and 1996 (S, N, T and W serials). As it is an uncontrolled process, it can have different outcomes in terms of color achieved and uniformity. The present example can be considered without a doubt an extremely successfully tropicalized specimen, with a very even and elegant tobacco tonality throughout all three counters. Furthermore, the luminous material has aged to a light ivory tone, which perfectly complements the tropical subdials. The presence of the original guarantee and box, and its provenance from one of the most important private collections in Asia further propel the timepiece to new heights of desirability.