Anyone hear of Fisher M-55

[matukid]

Does anyone know anything about a Fisher M-55 detector?
I had aquired this detector a couple months ago, It looks simular to a 1210X or 1212x with just one dial for discrimination and headphone jack. I could not find any info on net about it but I did see some other "M" series that were ground box locators. The M-55 I have says on it that it's a metal detector and not a ground box locator. Any info would be appreciated. I realy would like to find out how old it is.
Thanks matukid.

 

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[U.K. Brian]

I think its a 4.5kHz valve locator that was replaced by the M-96 more than ten years ago. Though they say metal detector your more likely to find it under "valve locator" in a search.
With the later model they added a ground balance and the design went more to that of the 1266 with an "s" shaft.