DAB model documentation needs clarification #666
Description
User Anna points out that the units of scale for the DAB model are in fact Å-3cm-1 and not unitless as stated in the documentation. This is because the scattering length density squared term is subsumed into the scale factor for this model.
One solution, which would probably break old project files, would be to change the interface and in fact pull out the square of the scattering length density term, as it is for most other models. This would leave the scale factor, if on absolute scale, to be directly related to the volume fraction of the phases and unitless.
The other alternative would be to clearly state at the beginning of the documentation, that despite the table suggesting the scale factor has no units, it in fact has the units of Å-3cm-1
Ideally, we would change the units in the table. However that is autogenerated, as in fact is the scale factor itself, by sasmodels so that this would require some design changes to sasmodels. This is probably the better long term solution as a number of other models, particularly the shape independent ones, have a similar issue. NOTE: This is related (but slightly different) to issue #607.
Anna also points out that besides giving the the effective meaning of the correlation length it would be helpful to also define it properly (mathematically).