Change default increment of deriv

Hello,

I try to use "deriv" function to analyze the slope of some signals, I'm using transient simulation, so X-axis is time. For "deriv" function, what is the default increment or step size of the derivative function? In output setup, I simply write:

deriv(v("/cout" ?result"tran-tran"))

"/cout" is the signal. I want to change the increment to 2ps or 20ps, how should I do it?

Thanks a lot!