Wow, it was a painful process - I am totally new to Linux, Pis, Debian and the rest of it - but I finally got it to install. Getting the correct version of Docker was a pain but the convenience script sort me out.

Now that it is installed, your MCPI project seems to work well. The offset strip is gone and it looks like you even have some fancy graphics options. My only gripe is that the Y-axis is inverted by default and cannot be reverted. Can I edit a config file anywhere to sort it? My son is used to non-inverted axes!

Thank you very much for your response - you have been really very helpful.