"I'm trying to use the RunControl panel to change dt, but it isn't working. What's going on?"
dt specifies the integration step size. NEURON's standard run system also has a parameter called steps_per_ms that controls the intervals at which points are plotted to graphs; its numerical value is shown in the field next to the "Points plotted/ms" button. Clearly these two parameters must be compatible, i.e. the interval between two points on a graph must contain a whole number of time steps. The design decision was that steps_per_ms would govern dt. It does this by means of a standard run system procedure called setdt() that adjusts dt as necessary to ensure that dt = 1/(steps_per_ms * i) where i is a positive integer. setdt() is executed in response to any of the following:
--changing the contents of the numerical field next to the "dt" or "Points plotted/ms" button