If you don't use the GUI, you can still use the d_lambda rule. Just save this code

/* Sets nseg in each section to an odd value so that its segments are no longer than d_lambda x the AC length constant at frequency freq in that section. Be sure to specify your own Ra and cm before calling geom_nseg() To understand why this works, and the advantages of using an odd value for nseg, see Hines, M.L. and Carnevale, N.T. NEURON: a tool for neuroscientists. The Neuroscientist 7:123-135, 2001. */ // these are reasonable values for most models freq = 100 // Hz, frequency at which AC length constant will be computed d_lambda = 0.1 func lambda_f() { local i, x1, x2, d1, d2, lam if (n3d() < 2) { return 1e5*sqrt(diam/(4*PI*$1*Ra*cm)) } // above was too inaccurate with large variation in 3d diameter // so now we use all 3-d points to get a better approximate lambda x1 = arc3d(0) d1 = diam3d(0) lam = 0 for i=1, n3d()-1 { x2 = arc3d(i) d2 = diam3d(i) lam += (x2 - x1)/sqrt(d1 + d2) x1 = x2 d1 = d2 } // length of the section in units of lambda lam *= sqrt(2) * 1e-5*sqrt(4*PI*$1*Ra*cm) return L/lam } proc geom_nseg() { soma area(0.5) // make sure diam reflects 3d points forall { nseg = int((L/(d_lambda*lambda_f(freq))+0.9)/2)*2 + 1 } }in a file called fixnseg.hoc

After specifying the topolgy, geometry, and biophysics of your model, execute the statements

xopen("fixnseg.hoc") geom_nseg()