I'm trying make sure that I am using the gsl_odeiv_control functions
correctly.

I'm modelling neurons and my variables have different scales. Voltage is
usually between -100 and 50 mV. The membrane current gating variables
stay between 0 and 1. Internal calcium concentration is usually between
0 and a few hundred micro molar.

Each time I read the descriptions of the gsl_odeiv_control functions I
become more convinced that the parameters eps_rel, a_y, and a_dydt are
there to excuse some error in variables and derivatives that are far
from zero. Is that correct?

Since I have no reason to care more about values close to zero (unless I
do some complicated remapping of the variable values) should I set
eps_rel, a_y, and a_dydt to 0?

Since my variables have different ranges should I use
gsl_odeiv_control_scaled_new with an appropriate eps_abs and scale_abs
set with something like 1 for internal calcium concentration, 0.3 for
membrane voltage, and 0.001 for all of the gating variables?