Tax is onerous when there was no tax before. I'm trying to understand how onerous our tax is compared to that one. The national archives has developed a convertor for this purpose. I don't think trying to understand how a historical tax affected people is a waste of time. It's quite interesting.The question makes no sense. The window tax was clearly onerous or nobody would have blocked off their windows. You are wasting your time trying to impose your modern sensibilities onto the people of that time.