I want to make a survey where by random either question A in group X or question B in group Y is shown. I think I could just use a hidden question of type equation "rand(1,2)" and show a question A if it was 1, question B if it was 2. But it does not work, it seems that the random number will be re-computed every time a new group is loaded. A bug or feature? If the latter, can I make something else, like taking last digit of seconds when the survey started?

You need to test for an existing value. If, for example, you have question code "random1", the equation would be:

Hi,
exactly. Each click changes the random number.

IF you create it as you did. Only {rand(1,2)}
To avoid this, use the construct that is shown here "more than 1000 times"
{if(is_empty(random),rand(1,2),random)}

Only as long as the random number is empty, it will be calculated. If not, it keeps its value.

Joffm

@tpartner beat me by two minutes.