Help please to translate into English Aviation tool Identification

[davy]

I have just been given this item and was hoping that any member could help identify what it is and what is was used for, I think it is from WW2 era and was Aviation tool. I have attached a few photos and photos from book which is in Japanese, any help would be appreciated.
thank you
Davy

 

[Uncle Frank]

When we get someone on line who can help with reading the Japanese , I think you will find this is a WWII Japanese aircraft sextant used to plot your location while over water , etc. It worked much the same way a shipboard sextants were used for many years.

 

[Mike Cash]

Bubble Sextant. There is a date of March 19, 1945 on one of the labels.