There's more than one way to do it. The first example uses the select command to access the records...

let setCnt := cnt(select YourTable);
let mean := sum((select YourTable).YourField) / setCnt;
let variance := sum((select YourTable).pow(YourField - Mean, 2)) / setCnt;
sqrt(variance)

This next example copies the numbers to an array...

let mySet := (select YourTable).YourField;
let setCnt := cnt(mySet);
let mean := sum(mySet) / setCnt;
let variance := sum(for i in range(0, setCnt) do
pow(item(mySet, i) - mean, 2)
end) / setCnt;
sqrt(variance)

There is also an example in the Webinar EN 2020 team with the database name 089_Statistics. These links might be helpful...

https://www.mathsisfun.com/data/standard-deviation-formulas.html

https://ninox.com/en/manual/calculations/reference-of-functions-and-language