Sensor history sometimes doesn't honor Display precision (or incorrectly rounds)

[oliv3r]

The problem

I have a few graph sensors, where due to one reason or another, the graphs don't properly honor the (default) precision setting, or some weird rounding happens that causes weird fluctuations.

The data is stored via recorder in postgresql instead of sqlite.

I see it with various different integrations, so not sure if that's related.

Could it be that internally something is using floats, and due to the lack of precision with floats something sometimes goes wrong, and thus when floats being used they should be rounded?

Two random examples Here we're talking KM, which is reported in whole KM by the integration (renault)/API

The strange thing is here, that this integration is supposedly running only once every 6 hours to update its values.

What version of Home Assistant Core has the issue?

core-2024.5.5

What was the last working version of Home Assistant Core?

No response

What type of installation are you running?

Home Assistant Container

Integration causing the issue

No response

Link to integration documentation on our website

No response

Diagnostics information

No response

Example YAML snippet

No response

Anything in the logs that might be useful for us?

No response

Additional information

No response

[karwosts]

This is floating point rounding error in calculating the statistics min/max/mean.

There's a related issue in frontend, but I don't know what the right answer is for a fix, if it should be in core, or frontend, or chart.js, or maybe this is not a bug at all.

https://github.com/home-assistant/frontend/issues/18982

Also display precision settings are only used for choosing the number of decimals when writing the state. It does not affect how the sensor values are plotted on charts.

[oliv3r]

Looking at the database, I see indeed the same thing.

 9123 |         | 1718082010.4386117 |          22 |       | 1718078400 | 83.03999999999999 | 83.04 | 83.04 |            |               |       |    
 9149 |         | 1718085610.4388337 |          22 |       | 1718082000 | 83.03999999999999 | 83.04 | 83.04 |            |               |       |    
 9175 |         |  1718089210.417186 |          22 |       | 1718085600 | 83.03999999999999 | 83.04 | 83.04 |            |               |       |    
 9201 |         |  1718092810.440033 |          22 |       | 1718089200 | 83.03999999999999 | 83.04 | 83.04 |            |               |       |    
 9228 |         | 1718096410.4281015 |          22 |       | 1718092800 | 83.03999999999999 | 83.04 | 83.04 |            |               |       |    
 9255 |         | 1718100010.4390285 |          22 |       | 1718096400 | 83.26130507151669 | 83.04 | 83.46 |            |               |       |    
 9282 |         |    1718103610.4422 |          22 |       | 1718100000 | 83.46000000000001 | 83.46 | 83.46 |            |               |       |    
 9309 |         |  1718107210.421433 |          22 |       | 1718103600 | 83.46000000000001 | 83.46 | 83.46 |            |               |       |    
 9336 |         | 1718110810.4408443 |          22 |       | 1718107200 | 83.46000000000001 | 83.46 | 83.46 |            |               |       |    
 9363 |         | 1718114410.4144876 |          22 |       | 1718110800 | 83.46000000000001 | 83.46 | 83.46 |            |               |       |    
 9390 |         | 1718118010.4440346 |          22 |       | 1718114400 | 83.46000000000001 | 83.46 | 83.46 |            |               |       |    
 9417 |         | 1718121610.4402826 |          22 |       | 1718118000 | 83.46000000000001 | 83.46 | 83.46 |            |               |       |    

[michaelarnauts]

I notice this with a sensor that has the same value, but at the time of a Home Assistant restart, it got the rounding error. Maybe this is a race condition where a value got in during startup and the precision wasn't loaded yet or something?

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