Hope this is useful
{note: trim=right}Weight in kilograms: {formtext: name=weight_kgs; default=; cols=3}{endnote: trim=yes}
{note: trim=right}Height in metres: {formtext: name=height_metre; default=; cols=4}{endnote: trim=yes}
{if: weight_kgs>0; trim=yes}Weight (in kg): {=weight_kgs}{endif}{if: height_metre>0}
Height (in metres): {=height_metre}{endif}{if: height_metre > 0 and weight_kgs > 0}
BMI: {=weight_kgs/(height_metre^2); format=.1f}{endif}