**Graph size**
Here you can choose the size of the graphs. Smaller size files load quickly,

with less resolution while large files show more resolution but load more slowly.

**Hold Coefficients Constant**
Here you can enter values to hold coefficients constant during fitting.

Leave the entry field blank to let the coefficient fit normally.

Note that coefficient bounds are overridden by holding a coefficient constant.

n

^{2}(x) = 1 + (B1 x

^{2})/(x

^{2}-C1) + (B2 x

^{2})/(x

^{2}-C2) + (B3 x

^{2})/(x

^{2}-C3)

**Estimated Initial Coefficients**
Here you can enter values for initial parameter estimates.

Few users will need this section, as the site estimates initial

parameters using the Differential Evolution genetic algorithm

for both nonlinear equations and non-Gaussian fitting targets.

n

^{2}(x) = 1 + (B1 x

^{2})/(x

^{2}-C1) + (B2 x

^{2})/(x

^{2}-C2) + (B3 x

^{2})/(x

^{2}-C3)

**Coefficients Bounds**
Here you can enter coefficient upper and lower bounds. Leave the

entry fields blank to let the coefficients fit without bounds.

Note that holding a coefficient constant overrides these bounds.

n

^{2}(x) = 1 + (B1 x

^{2})/(x

^{2}-C1) + (B2 x

^{2})/(x

^{2}-C2) + (B3 x

^{2})/(x

^{2}-C3)