WW2 Japanese Sighting Device

[Porcelain44]

Can you help me ID this item? It appears to be a WW2 Japanese sighting device of some kind.

[T. A. Gardner]

I don't think this is a sight for a weapon. The photos don't show the small bubble centering level in the white mounted on it clearly. I assume that's what that is. I also assume the eyepiece has the other end of the optics facing away from the blade through that horizontal tube. It's 4 power and has an 11.15 degree field of view, that's clear. The long blade looks more like a ruler than anything.

My first guess on this is it's either a quality control tool or possibly something used for surveying and map making. Maybe some sort of bore sighting / QC device used in larger gun manufacturing?

[Porcelain44]

Thanks for the info. There are a great many gird lines and numbers visible through the eyepiece. There is a horizontal level and another bubble-like circular device at the base of the eyepiece (on the slide).

[T. A. Gardner]

What you have is known as an Alidade or it is a surveying instrument for laying out the topography of a site. Yours would be used with a plane table to do this.

https://en.wikipedia.org/wiki/Plane_table

While the exact style of a plane table alidade varies, they look pretty much like this in use:





These are typically used for detailed map making and building site surveying.

The marks inside the telescopic sight piece are stadia and used in conjunction with the graded protractor along side it to measure distances to objects as well as their height above and below the plane of the table.