Hi,

I am quite new at flux language, and I have a question:

I have a simple dataset with just one value.

I am using a window to aggregate by a chosen interval and store the result in a table variable like this:

```
val=from(bucket: "myBucket")
|> range(start: v.timeRangeStart, stop: v.timeRangeStop)
|> filter(fn: (r) => r._measurement == "myMeasurement")
|> drop(columns:["_measurement"])
|> window(every: 5m)
```

Then, I can use significant functions for me, like min, max, mean and stddev like this:

```
minval=val
|> min()
|> set(key: "_field", value: "min")
maxval=val
|> max()
|> set(key: "_field", value: "max")
avgval=val
|> mean()
|> set(key: "_field", value: "avg")
sdval=val
|> stddev()
|> set(key: "_field", value: "stddev")
```

And to finish, I can concatenate all of this, polish up the windowing and make a nice representation:

```
union(tables: [minval, maxval, avgval, sdval])
|> duplicate(column: "_stop", as: "_time")
|> drop(columns:[ "_start", "_stop"])
|> pivot(rowKey: ["_time"], columnKey: ["_field"], valueColumn: "_value")
```

Now, I would like to calculate two different stddevs, the one above the mean, and the one under, like described there: https://jdmeducational.com/1-2-or-3-standard-deviations-above-or-below-the-mean/

It seems easy, all would need is something like this:

```
lowsdval=val
|> filter(fn: (r) => r._value < MEAN)
|> stddev()
```

I am very new to flux, and I did not find the way to do that (it is probably super simple).

I can do it easily with a constant like this (assuming the mean value is 50):

```
lowsdval=val
|> filter(fn: (r) => r._value < 50)
|> stddev()
```

Now, how can I achieve this with the value of the mean of the current window? It is even already calculated in the *avgval* table, so I suppose I just need to extract it from it with some syntax I missed.

Thank you in advance for any help or hint.