Certain attachments like this require a standard correction with different Minolta meters. I don't have the one you're describing, but with the Flashmeter III and 5-degree attachment, for instance, you need to reduce exposure by 1-1/3 stop from the reading. It's on the instruction sheet. I just adjust the ASA setting when I use this attachment. I think some of the later meters have settings to compensate automatically for different attachments. Once you know the correction factor, though, you can just apply it.