plotting HEMP E1 waveform based on IEC standard

Hi all,

I would like to plot HEMP E1 waveform based on the IEC standard, but i just don't understand why i cannot get the waveform based on the equation mentioned in the standard. I thought this is a simple equation to plot, but to my surprise, I cannot get the graph at all. Do I miss understand the meaning of the equation? It should be E01*k1*(exp(-a1*t)-exp(-b1*t)) right? By the way I m a little confuse on the variable to represent k1. It means 1.3? I sincerely hope that someone can help me.

Thank you