Duo 2v question. Underside compartment

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Hi There,

I have just brought a Duo 2v. On the underside is a compartment with 2 screws. I can't see this mentioned anywhere. You can see it in the attachment. At first I thought it was cracked but I think it's meant to be like that? Can someone confirm it's meant to have that line on it? And also what the cover covers!

Thanks.

Matthew