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In the land of Earthquakes I guess I shouldn't be surprised how many precision levels there are floating around. A while back I saw Keith Rucker working with a little version of this someone had sent him, and I thought "I'm here in Japan, I must have one!" This was one of the first ones I bought, it was sold cheaply (~$30 delivered) as 'Junk' because the person selling it (clearly not a machinist) couldn't find any 'level' places in their house with it and assumed it was broken.
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When the postman delivered it, he gave me a pointed look, which upon handing it over to me I almost dropped it on my feet and quickly understood. The thing is a solid casting and weighs a ton, his annoyance was pardonable. In my experience, it is an unusually large one at 300mm square, and is japanned in a lovely deep purple color that my iPhone wasn't able to really capture here.
The company, Fuji Seimitsu Keiki Seisakusho Co., Ltd. (now thankfully just
FSK) is
still making these levels, and even has rental and calibration services. To buy this one new (in this grade) is several thousand dollars, but I'll be the first to admit that the used market here is flooded with variations of this unit sold quite cheaply, although usually in smaller 150mm and 200mm sizes and in rougher shape. Conventional style engineers levels are also commonly seen, most of them use, like this one, the Japanese precision standard of 0.02mm/M indication, although I have a few with up to 0.01mm/M graduations (and certified accuracy.)
It came in the factory box, still wrapped in the original oil paper which preserved it nicely. This is no spring chicken, from the certification label inside the box lid it was made in Showa 45, which is 1970 for the rest of us. The measurements there are not totally intuitive, I don't know how it is done in the US, likely the same way, but most of those numbers are referring to tenths of a graduation. The chart shows measurements done from both directions in red and blue lines, I guess that bubble stiction can cause variation based on which way it is traveling, although mine doesn't seem to suffer from that. It shows deviation of 0.1 graduation or less across its range, or less than 6 microns of error over across its width (if I did my numbers right.)
The left and right sides are +2 and -3 microns off, making it a pretty useful square on its own. The top is 0.2 graduations off, and the V ways on the bottom is 0.3 graduations off. As of now, that makes this unit a top rated JIS Class AA, but the standards were not codified until 1993, so this predates that by a few years
Since getting this one, I've picked up quite a number of Japanese levels, not that they are of any great use to me at the moment, but they are kind of magical in their simplicity and self proving nature. Even this old $3 masons level is made with a beautiful casting that is easy on the eyes.
I only pick something up these days if it is highly unusual, as I justify all these unnecessary levels to myself as some kind of a 'collection', but truthfully it breaks my heart seeing them unloved and given away for a few dollars and I just have to pass them by.