Depends on the quality of your SPICE models. (https://en.wikipedia.org/wiki/SPICE https://en.wikipedia.org/wiki/SPICE) When you model by hand you typically use

Depends on the quality of your SPICE models. (https://en.wikipedia.org/wiki/SPICE https://en.wikipedia.org/wiki/SPICE) When you model by hand you typically use ideal models. SPICE models can be vastly more complex. A good example is a diode which is harder to model as it's a non-linear device. Simulated "electricity" (voltage and current) is reduced to a set of differential equations, which the program then uses to plot charts.