The formula generally takes the exponential form: $$ VCF = \exp\left[-\alpha \times \Delta t \times (1 + K_2 \times \Delta t)\right] $$
The ASTM standard uses a series of coefficients ($K_0, K_1, K_2$) to calculate the VCF. Astm Table 54b Excel
Creating an Excel Spreadsheet for ASTM Table 54B Calculations The formula generally takes the exponential form: $$