Folin–Ciocalteu formula
Authors mention that pyrogallol (PG), among other standards, has been purchased from Sigma Aldrich US and used as is without further dilution. The amounts of polyphenols were calculated as PG equivalent by external standard method, and utilizing additivity of absorption coefficients the proportion has been established.

$62.5$ is just a dilution factor for the herb extract probe. From the protocol, first time the extract was diluted $5$ times (from $\pu{5 mL}$ to $\pu{25 mL}$), second time – $12.5$ times (from $\pu{2 mL}$ to $\pu{25 mL}$), resulting in total dilution factor of $5 \cdot 12.5 = 62.5$.