Voltage clamp step onset behavior for continuous and stochastic channels. The step begins
at 1.985ms and the timestep is 0.02ms. This uses the midpoint evaluation method for the step,
(stepStyle="midpoint" in the voltage clamp)
so the effect is as if the step started at 1.980ms. This fugure should be compared with
the file run-onset-avg, which does the same calculation but with stepStyle="average" for the clamp.