Hi @colonus
first of all, there is a mistake in your form: you have 4 notes named show_high (the name must be unique).
The second thing is that your if statement should rather look like:
if((${a} > ${b} and ${a} > ${c}), '1', if((${b} > ${a} and ${b} > ${c}), '2', if((${c} > ${a} and ${c} > ${b}), '3', '4')))
Please let us know if it solves your problem.