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Hi Anil,

these movements are very similar - the 1120 is the earlier version of the 'Jet' Autodater using the circular geared automatic rotor, first made in 1962. I would guess they are essentially the same movement, with the 4100 being a later development first produced in 1964, with the main difference being that this one added a day wheel. The 1120 is date only (or no day or date) - this is evident from the greater depth of the 4100 movement (6.39mm) whilst the 1120 was 5.00mm. Both are 29mm wide.

The 4100 also had a different range of jeweling - it was 19,25 or 35, whilst the 1120 was 17, 21, 23, 25, 27 or 35 jewels.

The other difference is in dial logos - the 4100 is called the Autodater 'Seven', so you'll find a 7 logo or the word 'seven' on the dial, often also engraved on the case back. The 1120 is the 'Jet' autodater, with the word on the dial as well the Jet logo, also repeated on the caseback:



This pic shows the usual '7' logo on a 4121 ('Monthly') version of the 4100 series:




You can find a movement table I've compiled for the vintage Citizens if you are interested in this brand here:

http://seikoholics.yuku.com/sreply/1895

Sweephand
 
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