This example uses the delay data for an HB11-12MHz-50.
To calculate the delay at 62.5% of the cut-off frequency we find the normalized delay is 4Div below the reference of 2.5S. Each division is 0.5mS. Thus, the normalized delay is 2.5S minus 2S. Which is 500mS at 19.2 MHz. The cut-off frequency is 12 MHz.
Delay = (Time in seconds) / Fc – Cut off Frequency)
= (500)/(12*106)
= 41.67nS