Look at the DXO measurements shown in the graph
no, sorry... I never look at those DxO charts :-)
When set for an ISO of 100, the measured ISO of the P65+ is only 44. This means that if you expose according to the meter, the image will be underexposed by one stop
I can't replicate those values with my P45 and P21+.
I've just shot a BasICColor Grey card (see attachments).
My meter showed 30''/f4 for ISO50 (60''/f4 for ISO100 on the P21+).
Unlike other grey cards the BasICColor card reflects 25% grey (see attachment).
The respective Lab value is L*60.
Now, these are the shots from the P45 and P21+ without any adjusments made in Capture One (only WB); processed to TIF and opened in Photoshop.
Well, if you look at the Info palette in Photoshop I would say my meter works as supposed to... and so do the digibacks.
I don't use the meter anyway (at least rarely)... I mostly expose short of clipping highlights.
Don't know if this clarifies something with regard to DxO charts... it's simply just the outcome based on light metering and C1 processing...