I constantly come across threads where someone is arguing that this or that movement is inferior because of its lower beat rate. I held the same belief my first few months as an aspiring ‘WIS.’ However, as I learn more about mechanical movements, there appears to be little substance behind this perception. I would now actually prefer – all else being equal – a 21,600 bph or even 19,800 bph watch over a 28,000 bph watch.
1) Many high-end watches stick with 21,600, and ETA appears to be going back to the slower rate with their possible replacement to the venerable 28XX series. (See http://professionalwatches.com/2013/02/tissot_powermatic_80_hands-on.html)
2) In theory, a lower-beat movement has more positional variation, but who really thinks an adjusted 21,600 bph movement with a free-sprung balance can’t be nearly as accurate as a comparable 28,000 bph movement? Even a typical 2846 with a $30 regulation will usually outperform a comparable, base grade 2824. But the 2846 will have all the inherent advantages of a low-beat movement.
3) A low-beat movement is inherently more durable, requires less frequent servicing and is less sensitive to servicing neglect. The mainspring requires less tension, translating into less force on the gear train. The balance and escapement are able to move at a slower speed, also reducing wear and tear.
4) Greater inherent power reserve (all else being equal). (I haven’t worked out the math, but it looks like the power reserve difference between the 6r15 and 2824 is entirely due to the difference in beat rate)
5) Did 28,000 bph just become the standard because the Swiss were chasing quartz accuracy during the quartz revolution? An unnecessary arms and marketing race (like the depth rating on dive watches) with little thought (at least by consumers) about the negative consequences?
I would rather have greater power reserve and durability with less servicing than a movement that is theoretically 2 seconds more accurate. Mabe not 18,000, but 21,600 seems like a good engineering compromise. Am I wrong?