I think it might be an optical illusion Della. The 8 pointy star extends right to the edge of the disc. Its a lot plainer than the ones shown in the link.
I really must stop buying obscure bits of glass and stick to what I know

My "unknowns" shelf is getting too big.
Enjoy your stay in Devon and if you manage to get further down to the S.W. pop in for a cuppa

Keith you're a regular, you should have a lifetime membership for free!