What is this and how to use it?

[vitality]

Hello!
Yesterday won auction for an interesting plate holder (as I understand it is a plate holder), which has "curtains" inside.
http://i037.radikal.ru/1107/d9/5bcbfddacc32.jpg
If I understand correctly, this kind of holder was used to make exposure tests? (expose one line, then scroll to the next line, expose it with + or - and etc.?)

There is a hole drilled in lid (you can see it on picture) + dark slide has one hole as well. I have no idea what was the purpose of these 2 holes. May be it was supposed to be a "red window" in those holes? But what for? To see what "line" we are currently exposing?

[akfreak]

Looks like a glas plate holder and pressure plate with masks to create multiple panos on a single glass plate. Very interesting. Ah the holes they let you test in a bracketing type of way to test films or in this case glass plate emulsions! What is the overall size, is it 5x7

[vitality]

Looks like a glas plate holder and pressure plate with masks to create multiple panos on a single glass plate. Very interesting. Ah the holes they let you test in a bracketing type of way to test films or in this case glass plate emulsions! What is the overall size, is it 5x7

You mean drilled holes for bracketing type test? Or "holes" in curtain (mask?) (I understand this cut lines are made to do so) - this kind of test I know, but if you are talking about drilled holes (in lid and in dark slide) - I'm not familiar with this kind of test. :(

External size is approx. 30x26cm, according to what, I would say, that internal frame is smth like 5x7 size (I don't have it yet to measure).

I haven't seen before this kind of plate holders. Externally looks like usual single sided "wet plate era" holder, but with curtain-mask inside.