Fahrenheit is not an absolute scale, so there is nothing special about 0F, you're right about that. As for your other two examples (atmospheric CO2 and stock tickers)... Yes, the scale should start at 0. Why shouldn't they?
So if someone showed body temperature measured in Kelvin you would argue that it should start at 0? That seems even more ridiculous.
> Why shouldn't they?
Because for the vast majority of stock it would appear to be a straight line every single day? Can you find me a example of a stock trading app for a company who's price is > $100/share that shows intraday price activity on a zero scale?
Likewise most co2 charts start around 300ppm since that has been roughly where the lower bound of atmospheric co2 levels have been for all of human history.
The last time co2 was 0 on the planet earth it was just a molten rock so what's the meaning of showing this value? It's not even theoretically possible that co2 could be that low baring alien life sucking the atmosphere off the planet.
Can you clarify why the scale should start at 0 for these things? How is that anywhere close to an honest representation?
Because starting at zero can cause scaling issues that mask meaningful trends and variation. That can also be abused to mislead, but a simple rule like “always include zero” ain’t the solution to that.
All fair points about zero. Sorry, I acknowledge now I was overly influenced my metrics dashboards I use for alerting. I've seen people panic at a seeming steep rise in error rate or increase in latency because the chart was not showing the full range (0 to 1 for rates, or 0 to 2x SLA for latency). I was only thinking of operational alerting dashboards.
In that case, we should report body temperature in Kelvin. However, now the dead-alive range (95degF - 107degF) becomes 308K to 315K.
Starting at zero, that range (17K) is now only 5% of the graph, assuming we start at zero. Or in other words, if your chart is 10cm tall, the entirety of the useful range is compressed into a space that is 5mm tall.
