In the attached survey:
q1: Do you like ice cream?
-- Yes, always (code 100)
-- Sometimes (code 50)
-- No (code 0)

q2: Do you often eat ice cream? (only shown when previous answer was "Sometimes" of "Yes, always")
Relevance: !is_empty(q1) && q1 ne 0
-- Always (code 100)
-- Often (code 66)
-- Regularly (code 33)
-- Never (code 0)

q3: equation that should show "0" (zero) when q1 == 0 and otherwise: (q1+q2)/2
Using: {if(q1==0,q1,(q1+q2)/2)}

But it never shows "0". When I always show q1 (relevance =1), then it will work.
Does this mean that you cannot use hidden questions in equations?

Does anyone know a workaround?

See attached .lss and
lime25test.toolsforresearch.com/index.ph...553?lang=nl-informal

Usage of NAOK ....
www.limesurvey.org/manual/Expression_Manager#Usage_of_NAOK

When you put some variable from question in any equation : if this question (or subquestion) is hidden by condition : this disable all equation.

Then else q2 disable all equation.

Tested : limesurvey.sondages.pro/715553

Thanks Denis!