finding NM by writing formulla in hspice
after some research, I found two ways in order to find when derivate of a parameter is -1.
First way is using commands for example:
.MEAS dc vol find v(out) when deriv ('v(out)')=-1
It's just an example to show the syntax and based on your project the input and output nodes might be different.
The second way is to use CosmosScope or any other wave viewer application.

In this way using &quot;point to point measurement&quot; calculation of slope can be done graphically, but sometimes take some time to achieve proper response.
Best of luck