**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) + Offset

**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 non-linear 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) + Offset

**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) + Offset