Automatic numbering for individuals: Circular dependency

Dear OF team,

I would like to implement autonumbering for tree individuals such as in this post: https://www.openforis.support/questions/2681/start-value-for-automatic-numbering The field 'num' containing the automatised numbering of tree individuals should not be visible in the data entry form.

I implemented two lines of code:

(1) Constant value = 1

(2) Expression = 'math:max(parent()/a_in_ind/num)+1' apply when 'count(parent()/a_in_ind) > 1'

Adding the first individual works fine but when adding a second, OF runs into the following error: 'Circular dependency found in graph for node /transect/a_in_ind[2]/num'

Thus far, my workaround is to have the 'num' field not calculated, with the very same default expression as mentioned above: 'math:max(parent()/a_in_ind/num)+1'. This works perfectly fine but leaves the 'num' field editable in the data entry, which is a possible source of error, if accidentally modified.

Thanks for any help regarding this problem.

Best, Jan