html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/issues/5597#issuecomment-879561954,https://api.github.com/repos/pydata/xarray/issues/5597,879561954,MDEyOklzc3VlQ29tbWVudDg3OTU2MTk1NA==,1217238,2021-07-14T03:43:37Z,2021-07-14T03:44:00Z,MEMBER,"Thanks for sharing the subset netCDF file, that is very helpful for debugging indeed!

The weird thing is that the dtype picking logic _seems_ to have a special case that, per the code comment, suggesting we want to be using float64 here:
https://github.com/pydata/xarray/blob/eea76733770be03e78a0834803291659136bca31/xarray/coding/variables.py#L231-L238

But in fact, the dtype picking logic doesn't do that, because the dtype is already converted into float32, first. The culprit seems to be this line in CFMaskCoder, which promotes the dtype to float32 to fit a fill-value of NaN:
https://github.com/pydata/xarray/blob/eea76733770be03e78a0834803291659136bca31/xarray/coding/variables.py#L202

To fix this, I think logic in `_choose_float_dtype` should be updated to look at `encoding['dtype']` (if available) instead of `dtype`, in order to understand how the data was originally stored.","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,942738904
https://github.com/pydata/xarray/issues/5597#issuecomment-879361320,https://api.github.com/repos/pydata/xarray/issues/5597,879361320,MDEyOklzc3VlQ29tbWVudDg3OTM2MTMyMA==,1217238,2021-07-13T19:58:39Z,2021-07-13T19:58:39Z,MEMBER,"This may just be the expected floating point error from using float32:
```
In [5]: import numpy as np

In [6]: -32766 * np.float32(625.6492454183389) + np.float32(20500023.17537729)
Out[6]: 1.2984619140625
```

If you use full float64, then the data does decode to 0.0:
```
In [7]: -32766 * np.float64(625.6492454183389) + np.float64(20500023.17537729)
Out[7]: 0.0
```

So the question then is why this ends up being decoded using float32 instead of float64, and if that logic should be adjusted or made customizable:
https://github.com/pydata/xarray/blob/eea76733770be03e78a0834803291659136bca31/xarray/coding/variables.py#L225","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,942738904