Thank you @bob.bernstein, that makes sense to me. I did make a mistake there. I get it now. I appreciate you setting me straight.
My advice is to make sure you know the dots per inch that you'll be printing at. If you want to print to scale, you'll need to render with that in mind as well which can be tricky. To verify the lengths, you can still use the Bobo script and print the dimensions to check with a ruler after printing.
If your printer prints at say 200 DPI, then you'll need 200 pixels of render space per inch. Let's say the whole housing is 10 inches across, then you need 2000 pixels of printed area which will be impacted by the camera zoom/level. If you plan on printing to a 8.5 x 11 piece of paper, in pixels @ 200 dpi that would be 1700 x 2200 pixels. (You can use the print size wizard as well to work out the DPI.) If you have .5 inch margins around the edges of your paper, then you'd render at 1500 x 2000. Some printers can print to the edge of the page, so you can set 1700 x 2200 in that case. (Or use Print Actual Size or Scaling 100% in the print properties out of the printing application.)
But you still have to zoom properly to get it to render at the right size. You may have to experiment, but I'd try the following.
1) Make a 8.5in by 11in plane and put it under your object. Maybe make it not renderable in the object properties.
2) Center it under your model
3) Press F10 for the common render settings, set the resolution to 1700 x 2200 (assuming 200 dpi in this example with Print Actual Size or 100% scale)
4) Go to your top viewport and zoom in until the edges of your plane fill the frame perfectly. Or, if you prefer a camera, use a camera rotated exactly 90 degrees downward and a very low FOV. (like, .1)
5) Render and print. Check the DIMaster measurement against a ruler to ensure they are the right size. If not, zoom as needed, renderer and re-print. If you know you are going to do this a lot, save that scene for use with future objects.
It's a bit janky of a process, I do think this would work though.
Best Regards,