The first number indicates the range - so at one time there's normally one XXX, one 1XXX, one 2XXX and so on... When they do a refresh of the hardware they bump the number up by 100.
So there was a 1600, then a replacement 1700 and now the 1800 ISR...
Same with the 2500, 2600, then 2800 (here they skipped 2000 so they line up with the 3800 and 1800)...
So there seems to be some kind of fuzzy marketing related logic there. Since they're now happy to skip numbers I suppose someone must've come up with a good idea for what to do when after the 1900,2900, and 3900 :-)
The switches are numbered seperately, and tend to be a little more random...
Aaron
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