Does the calculation of the new hawl for zakat begin with the price of the silver nisab on the day the zakat is disbursed, or with the price of the previous year, given that the silver nisab changes daily?

If the value of the money reaches the niṣāb of gold (85 grams) or silver (595 grams), Zakāh becomes obligatory upon the completion of one full Hijri year, provided it remains at that niṣāb. One-quarter of one-tenth (2.5%) of the money on which Zakāh is due is to be given. However, if the money falls below the niṣāb during the year, a new year is started from the moment it reaches the niṣāb again.