What kind of Leica-Meter is this?

[avid1]

I bought a German TLR camera recently and this Leica-Meter was included. I am not sure if this is part of something more elaborate or what, because I can't see how this works as is. It came in that vintage leather pouch and that's it. I have 3 other light meters, so I am not very keen on this, but would like to know what it is anyway! Couldn't find anything about it online, so here I am asking for your help to identify this instrument. Thanks

 

[choiliefan]

This is a low-light booster which attaches to your Leica-Meter to increase sensitivity.

 

[avid1]

This is a low-light booster which attaches to your Leica-Meter to increase sensitivity.

Ah, I see. Thanks. I guess it is of no use without a Leica-Meter itself.