[Grayscale for color value comparison]

Here’s a shot of what I’m looking for. This is from photoshop. 

[Grayscale for color value comparison]

I’m new to Affinity. Is there a way to add a grayscale and then pull color from a photo to match/determine the proper value? I’d like to see the colors next to the various value levels of the scale. So far, I’ve just been able to convert the whole photo to grayscale but want to be able to compare the colors. Thanks.