I recently found a Gossen Variosix Electronic light meter (also known as the Gossen Polysix) at a thrift store. Unfortunately, the battery compartment won't open. I turn the thing on the bottom but the compartment does not loosen.
It's important to note that the enite back is supposed to come off. 

![Gif of problem](https://imgur.com/kllXXgb.gif)