Thanks everyone for your feedback and thanks to
@Tom Kindlon for sharing.
Most, if not all, of the criticisms here are valid. This is why I am sharing it. I needed a larger pool of feedback.
The starting point of the scale was defining what 100% can do and than halving it. I chose to halve for each descriptor as an easy way for people to relate to the impact of ME on people. Some people can relate to percentages easily but most people can relate to halving more easily.
So, as I said, I started with 100%. This is divided into hours of activity and is based on an idea of total available energy for a week. The scale base is simple but how to explain it is what has become increasingly complicated. I see here that some people are looking at it in terms of levels and fitting descriptors rather than using it as a guide and getting a feel for how their capacity fits on a percentage scale. I am not sure how to help people with ME get the best use out of the scale.
I divided this energy into four categories:
Work - Moderate - Light - Nothing
Technically, I feel that there should be a category between light and nothing but this introduced complexity that I wanted to avoid (the implications of this have come up in some comments).
So, I start by basically explaining what these hours are at 100% and then dividing by 2... My main objective early on is to illustrate how reducing capacity can impact people. In particular, the relationship between "work" and "home". I want to get readers to think about how much capacity they actually have as this will tell them where they fit on the scale.
Another issue with interpretations of the scale is people tend to be more aware of their daily activities rather than their total weekly activity (which the scale is based on as it averages out daily fluctuations).
So my first task is to try and get people looking at the scale in the right way (if we can). Initially, I would like to avoid nit picking the descriptors if we can. We can then go onto the descriptors.
P.S. I agree that this is not scientific, but you have to start with an hypothesis before you can test it. The hypothesis here is that most of the limitations that people experience are a result of an impairment in their energy system. Even if it is not technically correct it could be an analogy that is close enough to what people experience to provide a working model.
P.P.S. I agree with the step count comments but I would like to address this separately/in the future. I think that step counts are potentially a very helpful indicator of overall available energy. Technically, the idea behind them is an adjunct to the main hypothesis but that doesn't mean that they can't be useful.