I want to use the standard value for simulation purposes. The double exponential signal in CST Studio Suite has the form:

f (t) = A (exp (-t / B) - exp (-t / C))

A: Amplitude

B: Tfall

C: Trise

B=(50/ln(2))us & C=(1.2/5)us..... these are the standard values that I have taken after verifying various literatures. My question is regarding the value for "A" in the expression. Can anybody tell me the standard value for A for HV Lightning test waveform? Please help me in this regard.