yes, its right in front mounted to the ceiling. I get a vertical trapezoid. Its subtle, but would like to get it perfectly straight so i can put up a screen border
If you’ve already tried calibrating and still get the trapezoid, try calibrating it tilted in the opposite direction. To do this put a piece of paper (folded a few times if needed to gain some height) under the PPM at either the back or the front of the PPM to lift or lower the image. When the image is straight, calibrate it, then remove the paper.
Disclaimer:
I could be making a mental error and have it reversed in my head here, don’t have the PPM with me to test the directions. But in any case, the general steps should work, you only need to fiddle with which side to calibrate it on. If what I said above only makes it worse, then when you find the optimum setting, move the piece of paper to the opposite side (from front to back or vice versa) and then calibrate.
There are so many factors affecting the shape of the projection - roll, yaw, pitch. It’s especially hard if you have a bordered screen because you’ll see clearly if it’s not perfect.
Ywah it’s not easy, which is why the border has to be pitch black, absorbing as much light as possible, enabling you to oversize the image ever so slightly. The same way as the old crt televisions overscanned (and to some extent lcd TVs of today). There’s a reason why television is mastered with “title safe margins” which means that no important info is supposed to be close to the edges. A computer display output will immediately reveal the geometry errors though… 
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I agree with all of you, it’s not simple to get a perfectly rectangular image.
But keep in mind that the PPM is a pico projector whose main vocations are to be portable, to be implemented quickly and under very diverse conditions.
Therefore, wanting to put it permanently, with a border screen, is almost nonsense …
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I agree, as I have another much more capable home cinema projector - but I can totally see first time projector owners doing something like this just to get started. It’s a lot less money than where I started way back in the later nineties with a “cheap” ~4kEUR projector
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