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The ETA caliber 2870 is a vintage 3-hand Swiss made automatic movement that started production in the 1970s. This caliber is related to the ETA 2800 series of movements which includes the ubiquitous 2824-2 workhorse, but there are differences due to it being sold as a more economical movement. Interestingly, despite any architectural/part differences, the dial feet positions carry over to other ETA calibers.
ETA 2870 VS. 2871:
There is a similar caliber 2871 which beats at a lower rate. The 2870 has a beat rate of 28,800 bph 4 Hz, and the 2871 beats at 21,600, 3Hz.
Other Similar Calibers:
The 2870 has two siblings in this family of movements: the 2872 and 2878. The notable differences are outlined below.
The ETA caliber 2850 is a manual wind version with the same 28,800 bph and day/date features.
The ETA 2870 was originally sold as a non-hacking movement with an optional hack feature (hacking means the seconds hand stops when the crown is pulled out to time-setting position). This means that if you have a 2870 without hacking, you should be able to add a part to get hacking functionality. The hacking part you need is called a stop lever, ETA part number 9433. This part number is the same on many ETA movements, so it is easy to find on eBay or other sites.
The fine timing device (regulator) was also optional when ordering the ebauches from ETA.