This sale is for a Mamiya RB67 / RZ67 Eye Correction Lens +1.0 Dioptre for the standard RB and RZ type L2 and PD prisms, and the RZ67 Pro and Pro II AE prisms, complete with original (but wrong) box – the box says +2, but it is a +1 dioptre.
This dioptre simply clips into the prism viewfinder. This dioptre is very clean with no signs of use – it may never have been used.