Confusion about Custom Units in MathCad Prime 2.0

I often use MathCad to write documents that contain "usable math". Right now, I'm writing a document that involves Image files, file sizes, transfer rates, etc. I want to create a unit "B" (or "Byte"), maybe define MB as a mega-byte, and so on. So I might say an image is 640B * 480 = 0.3072 MB.

What I'm trying to do is to create a unit that is like a "counter", such as the "degree" unit, that I can attach to a quantity and have it "stick" to the quantity as a label. Reading the Custom Units "Help", I'm pretty sure that if I can figure out how to create a Byte unit, I can figure out MegaByte. However, the "dB" example in the Help menu gives me a bit of pause because applying the dB "unit" causes the unit label itself to disappear! I'd want something like the following -- I type 640*480 B (attaching a Byte unit label) and get 307200 B (OK, so far). I then replace the unit B with the unit MB and have the result transform to 0.3072 MB.

I don't know if this is, indeed, possible in MathCad Prime 2.0. If it is, that's wonderful, and I'd love to know how to do it. If it is not (yet) possible, I'd like to suggest adding this functionality to MathCad, as it will make it even more flexible to those of us who use it to create documents that include useful math.