Have you seen this helpful Bronica ETR - ETRS - ETRSi webpage?

Having purchased a used ETRS recently I was pleased to discover a webpage that explains the differences between the different models

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http://www.smu.edu/~rmonagha/bronetr.html

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Hope you might find it helpful. Perhaps the webmaster of this site could add a hyperlink to the above URL.

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The rest of the website seems to contain a considerable amount of info that should be of interest to medium format enthusiasts with other cameras.

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NB - I am not connected in anyway with the above website.