2500B vs. 2500C
: What's the difference between the 2500B and
: 2500C
: movement? I'm curious because I own an AT as
: well.
2500B beats at 28,800 beats per hour, or 8 beats per second (8 x 60 x 60 = 28,800). 2500C beats at 25,200 beats per hour, or 7 beats per second. Also, 2500C has a modified lift angle which makes production easier and also more closely aligns with the recommendations of George Daniels (the watchmaker who created the co-axial escapement). In fact, Mr. Daniels also recommended the lower beat rate in 2500C. That's why I suspect that Omega will stop at the C version, since this is also the version in every Planet Ocean model ever produced.
2500C has a longer power reserve (about 3.5 hours longer) than 2500B since it is beating more slowly. The watch also isn't working as hard since it is beating more slowly, so 2500C could potentially see greater longevity (this obviously has not been studied yet, since 2500C is far too new).
One thing of interest about these two movements - many people think of a "sweeping second hand" as being in constant motion. In fact, in the case of 2500B, you actually see 8 tiny jumps per second (each one corresponding to one of the "beats", or vibrations, of the rotor). The same is true of caliber 1120 in the Seamasters, since this watch has the same beat rate. These tiny jumps create the illusion of constant motion to the untrained eye.
By comparison, 2500C has 7 tiny jumps per second to create its sweeping second hand motion, since it beats at 7 vibrations per second.
