Thank you for your response, but it still is not clear which is the correct way to run a simulation in PVsyst for a horizontal single-axis tracker w/ a fixed tilt (saw-tooth type, SAT). Option 1: Choosing a "Tracking tilt or horiz. N-S axis" simulation and choosing the tilt angle (10 deg) Option 2: "Tracking two axis, N-S" and setting the max/min frame angle (both to 10 deg). We understand that you can fix the tilt by defining the "max/min tilt of the frame" to 10 deg for a two axis system, but doing this results in a different annual energy production in MWh/yr than running option 1 (option 2 results in ~7 % increase in energy production). For this reason, we are trying to understand the difference in the algorithms that PVsyst is assuming between the (2) simulations, which must be causing the 7% difference in energy production. That is a significant amount, especially when you might need to guarantee the annual energy production in order to meet a PPA requirements as an engineering firm designing a project. Also, the project site latitude is 35°15'16.63"N. Thanks!