Ah, that’s a tricky one. When you select a unit like “cm”, you need to have a defined monitor. That is, PsychoPy needs to know both the resolution of your screen and its physical dimensions. It is actually impossible to get this information for participants on Pavlovia, or really any other web-based system. You can get the resolution easily enough, but physical dimensions are not readable. So, unfortunately, you won’t be able to get consistent sizing across different screens unless each one has its monitor information entered into PsychoPy, and it’s simply not possible to do over Pavlovia at all.