Measuring using PPI is bass-ackwards. You're measuring a real-life piece of printed material in MM or Inches, then converting it to PPI, then printing at a set DPI, NOT PPI. Why even bring PPI into the picture? There's no reason to dick around with PPI. If something's XXmm x XXmm in real life, then create a file with those measurements and set the desired resolution (DPI). There's no added accuracy in converting to PPI. In fact, conversions like that just leave greater margin for error.
Pixel count is only useful when it comes to digital presentation, same as RGB color mode. Neither are of any value for print media, which is what we're creating here.
• Print media resolution is measured in DPI, not PPI.
• Print color is mixed via CMYK, not RGB.
• Monitors display in PPI, not DPI and that number isn't static. I.e. different monitors display at different resolutions.
• Monitors display in and mix colors via RGB, not CMYK.
Working on print media in RGB and PPI is incorrect. It results in poor and incorrect color output (RGB can display colors that CANNOT be printed via CMYK) and causes all these print scale issues that everyone has all the time.
