What does "use same aspect as pixels" button do?

[redrobin]

@raghukamath

If you want to have more fun set the dpi while creating the document to what your monitors native dpi. For example if you monitor has 96 dpi set the document to 96dpi, so now your document should have 96 pixels for 1 inch. Now when the documents dpi matches to that of your monitors there is no different in real life size and size on the monitor so this button should not affect the zoom on canvas

Hi there … maybe you can help me out, I’m not very techie but want to work out the ppi of my screen.
I’m using a Samsung M7 4k monitor and googled specs to show it uses 3840×2160 (137,68 ppi … some sites round it off to 140ppi).
However currently from my laptop it only outputs FHD 1920 x 1080 … so I’m assuming that effects the actual displays active ppi?

• Active Display Size (HxV) (mm)*697.31 x 392.23mm
• Aspect Ratio: 16:9
  Display Diagonal = 32" (31.5 in / 800.1 mm)
  Pixel Pitch: 0.182 mm
  Refresh Rate: 60 Hz

How would one recalculate that … would you know?
TIA