Eye dropper not reading grey scale correctly

[nmoran]

I have an image of a series of stepped blocks of grey tones going from fully black (100%) to white (0%). This is a .psd file that I have opened in Affinity. I decided I would measure the tones for accuracy before printing . Using the eye dropper tool and the greyscale colour model in the info window I started with the 0% tone (white). It reads as 0% in the info window so it is white.I measuered the 5% grey tone it reads as 5% ,so it is correct.  I measure the 10% block of grey tone it measures as 8% ,20% measures as 17% ,30% grey is 25% ,40% block as 33% and so on and so forth up to the 100% grey tone (black).I have attached the image/file I am measuring.I would love to know what the issue is here. I have incidentally opened this image some years ago in photoshop and all grey tones measured correctly.Any help would be appreciated.Nick

half letter 3-step tab test.psd

Edited January 21, 2023 by nmoran

[R C-R]

If I add grey quick shapes like rectangles or ellipses to the document set to 10% increments, they do not match the greys in your file. I assume this has something to do with opening the PDF document in Affinity, but I am not sure how.

Anyway, the greys shapes I added do show the correct 10% increment values in the info panel.

[lacerto]

Obsolete.

[nmoran]

Thank you very much both for the imput. I have opened lacerto's converted version.Most of the measurments match but as you pointed out there does seem to be some kind of rounding discrepancy here and there. The eyedropper measures 50% in some areas of the midtone greytone but 51% in other areas.This won't prevent me from proceeding as it negligable. Colour managment etc is something I would like to know more about though. Thanks again

Edited January 22, 2023 by nmoran

[lacerto]

Obsolete.