Dumb Question - Blind Device Convention

Hi,
This is an extremely stupid question, but I wanted to check what seemed to be obvious to me. I have written a plugin to control Velux Blind devices, and my presumption is that 100%/On should be closed and 0%/Off should be open. The Velux app (and API) operates the other way around and I am just about to adjust for the behaviour but wanted to check that I am not missing something. What is the normal convention ?
Neil

On is open. Think of it as controlling the amount of light. Max light is 100% open.


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Thanks - and the good news is it saves me effort