Suggestion for kWh display graph -- option to lock y-axis at 0

davei · 2019-10-27T22:49:16.154Z

Hi,
I run the Emoncms app on an old phone to monitor power use now that I have everything working, One thing that would improve daily energy use monitoring is to have a setting to set the minimum on the y-axis of the bar plot to 0. It currently auto-scales, so as energy builds up through the day th graph is changing.

This might be what people want when looking at slight variations in energy use, but I would like to lock the y axis minimum at 0, and then auto scale the maximum based on the visible timeframe. If I’m tracking along at 20kWh, 21kWh, 20.5kWh etc then I can see that all is good from a distance.

I haven’t written android apps, so I don’t know how much work is involved, but could this be a selector switch in the Page Settings screen?

Thanks.

Robert.Wall · 2019-10-28T00:58:09.232Z

Welcome, Dave, to the OEM forum.

Just looking at your proposal, you say you want to be able to see that all is well from a distance. What concerns me is, if the scale is automatic for the maximum as you suggest, you’ll not be able to see, without getting close so that you can read the vertical scale, what the absolute magnitude of what you’re looking at represents. My feeling is the graph/bar chart (this surely applies to both) should default to automatic on start-up, but you should be able to fix and retain both maximum and minimum Y-values. Charts in LibreOffice Calc do that, and it works. That way, a quick glance is all that you need to evaluate the present situation.

davei · 2019-10-28T01:12:10.821Z

Hi Robert, by “at a distance” I really mean as I am walking past the display, rather than stopping and concentrating. The plot just after midnight is what I’m hoping to have (since the 0kWh scales the graph nicely). If all bars are the same then I know something isn’t burning through the power, and if there is a trend upwards then I can have a closer look.

Graphs with distorted axes are a pet peeve of mine (such as political polling ones that show a massive difference of 0.5% by plotting from 49.0% to 51.0%).

I’m all for choice, so that’s why I thought a switch might be the best way of implementing this.

Robert.Wall · 2019-10-28T11:27:19.960Z

What I had in mind was a minimum value and a maximum value, both optional. So no value means auto, a value fixes that end of the scale.

davei · 2019-10-28T11:34:12.470Z

Hi Robert, that sounds good to me.

Cheers,
David.

Robert.Wall · 2019-10-28T11:59:05.635Z

Now you need @TrystanLea to pick it up and run with it.