Por eso te digo que he oído muchas explicaciones, y nadie me ha conseguido convencer. Estoy igual que tú, y no tengo conocimientos de buceo suficientes como para ofrecer una explicación convincente.
Sí te digo la verdad, a mi se me antoja que algún reloj vintage (p. ej. algún submariner), llevaba por algún mativo particular esta escala temporal y a partir de entonces se ha ido repitiendo de forma repetitiva hasta nuestros días.
Esto proviene de la wikipedia (sí, ya sé que no es una referencia como para presumir, pero tampoco tiene mala pinta):
Bezel markings[edit source | editbeta]
Most contemporary dive watches with conspicuous 15 or 20 minute markings on their bezels are the result of copying a Rolex bezel design of the 1950s. Back then divers typically planned a dive to a certain maximum depth based on now obsolete US Navy dive tables, and dived according to the planned dive profile. If the dive profile allowed a bottom time of 35 minutes the diver, upon entering the water, would set the marker on the bezel, 35 minutes ahead of the minute hand. The diver calculated this with the 60 - bottom time formulae (60 - 35 = 25, for 35 minutes bottom time the diver would align the 25 minute bezel-mark with the minute hand). Once the minute hand reached the main-marker on the bezel the diver would begin his ascent to the surface. The 15 or 20 minute scale helped with timing the ascent and whatever safety stop the diver deemed necessary. For contemporary diving methods the 15 or 20 minute "count-down" bezel is quite antiquated.[SUP][20]
Y esta explicación va más hacia lo que comentas:
I'm not sure how you're deriving your bottom times, but many dives last much longer than 20 minutes. In fact the shallower you dive, the more time you're allowed, provided you have enough breathing mix. A 60 foot dive will allow for a 60 minute bottom time.
The 15 minute marks are for detailed timing when increments of less than 5 minutes are needed. In traditional table diving, all dive times are in 5 minute intervals, so having a fully marked bezel isn't really necessary for the majority of the dive.
The bezel can be used in two ways, count-down or time-elapsed. When used in a count-down manner, the bezel pip is placed where the dive should end. For example, you plan a dive to 80 feet for 40 minutes. You align the minute hand with the "20" on the bezel. When the minute hand reaches the bezel pip(40 minutes elapsed), the dive is over and the 15 minute scale is right there to time whatever deco or safety stops deemed necessary, without having to further rotate the bezel.
When using the bezel in a time-elapsed manner, the pip is placed on the minute hand marking the time where the dive began. Using the same 80 feet for 40 minute profile, the dive ends when the minute hand reaches the 40 minute mark on the bezel. The only difference here is that you'll need to rotate the bezel "20 minutes" in order to use the 15 minute scale.[/SUP]
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