Join a MySQL table to itself + Operation

I receive free updates for some forex currency pairs. I am trying to calculate the other pairs by deduction from those with anumerator and a denominator.

my MyQSL table (named param_forex):

my MySQL query

    UPDATE `param_forex` as pf
    JOIN `param_forex` as pf1 on pf1.numerator = pf.Ticker
    JOIN `param_forex` as pf2 on pf2.denominator = pf.Ticker
    SET pf.Rate = (SELECT pf1.`Rate` WHERE pf1.`Ticker`= pf1.numerator / SELECT pf2.`Rate` WHERE pf2.`Ticker`= pf2.denominator)
    WHERE pf.Source='Calc'

Result : 0 rows affected. (Query took 0.0007 seconds.)
The expected output is for each line where the source is 'calc' to do the numerator divided by the denominator by fetching the appropriate values matching in the ticker columns and put the result in the rate column

I don't understand why it won't work, and I have spent hours on it.
(for those who have replied to a couple of my questions before, I hope you notice my queries are getting better...)

You don't need the subquery, just use pf1.Rate and pf2.Rate directly in the SET clause.

You also have your ON conditions backwards, since numerator and denominator are only set in the rows with Source = Calc.

UPDATE `param_forex` as pf
JOIN `param_forex` as pf1 on pf.numerator = pf1.Ticker
JOIN `param_forex` as pf2 on pf.denominator = pf2.Ticker
SET pf.Rate = pf1.Rate / pf2.Rate
WHERE pf.Source='Calc'