switch has an arbitrary number of parameters, which are alternating a condition and a result. If the first parameter is true, the result of the second parameter will be returned. Otherwise, if the third parameter is true, the result of the fourth parameter will be returned, and so on. For example:
switch([Bib]<100;"A";[Bib]<200;"B";[Bib]<300;"C")
If the bib number is less than 100, A will be returned. If the bib number is less than 200 (but greater or equal 100), B will be returned. If the bib number is less than 300 (but greater or equal 200), C will be returned. If the bib number is greater or equal 300, NULL will be returned.