Recommendations on complex optional fields
I have a unit conversion calculator (responsive web), and would like to add the optional ability to convert from weight to volume. Doing so requires the density of the substance, which I am deriving from an equivalent weight and volume of the substance. Because entering the density information for conversion is more confusing for people wanting to do simple conversions, I would prefer that the default option leans toward not converting. That is, if the user does not want to think about entering additional information, they can still easily do simple conversions.
The related fields are marked with red in the screenshot below. Basically, the default value should be the same as the units selected at the top of the form.
Because the default value is based on the units selected, the default value is dynamic. I have been considering a number of options, including:
- An advanced section for the form. The user can toggle a section of the form for "power users". When the advanced section is disabled, the features would simply be bypassed. An "advanced section" is somewhat ambiguous though, and doesn't really feel right to me.
- A toggle-switch (see image below) replacing the "destination measurement" field where the label is dynamic. The label could be something like "convert to XYZ", where XYZ is the measurement (weight/volume) that the user did not select above. For example, if the user selected "teaspoons" and the toggle-switch says "convert to weight". When selected, the conversion fields (weight/volume units/amount) are shown. My concern here is that I find toggle-switches to be odd in forms. I find them to be more appropriate for application/mobile device settings than for forms.
Am I missing a good way of toggling these optional fields?
References
Related questions
UX for a system that converts between units of weight and volume
The mobile view of the calculator in question
Example of a toggle-switch
