It's really two overlapping pie charts, each hand forming a side of a slice with an imaginary line from the center to the top forming the other side. We read them together, but to work as pie charts they have to be read separately.
You can't get much useful information from the hands' relationship to each other without knowing their relationship to the imaginary up line. If I say, "The hour and minute hands are 30° apart", what does that tell you about the distribution of time into past and future?
The hour hand shows distribution of hours between most recent 12 and next 12 into past and future. The minute hand is an entirely separate chart showing the distribution of minutes in the current hour into past and future.
Trying to read a clock from the frame of a pie chart is kind of confusing though, given this overlap. I don't think I would call it a good pie chart, much less the most perfect one.
Imagine Douglas Adams thinking that within a single generation, digital clocks would render the majority of smart, technical people adult people to not only be unable to read a clock but also unable to grasp the idea of fractions, ratios, time elapsed or remaining, or the concrete nature of the way days occur in the physical world.
You can't get much useful information from the hands' relationship to each other without knowing their relationship to the imaginary up line. If I say, "The hour and minute hands are 30° apart", what does that tell you about the distribution of time into past and future?
The hour hand shows distribution of hours between most recent 12 and next 12 into past and future. The minute hand is an entirely separate chart showing the distribution of minutes in the current hour into past and future.
Trying to read a clock from the frame of a pie chart is kind of confusing though, given this overlap. I don't think I would call it a good pie chart, much less the most perfect one.