Parameter AbsErrorMax defines the error tolerance of HydPy-Dam. At the moment (HydPy Version 4.0), we calculate its value based on the catchment size and the simulation step size as follows:

INIT * catchment area * 1000.0 / seconds

INIT is 0.01. So, for a catchment area of 77 km² and a simulation step size of 1 h, the error tolerance is 0.2 m³/s.

We encountered a case where HydPy-Dam actually achieved only this tolerance during low flow conditions due to an (only slightly smoothed) threshold behaviour. The simulated outflow looked like this:

Of course, the user can define an alternative error tolerance. But we should better provide defaults that always prioritise numerical accuracy over runtime efficiency.