how can i apply an expression on a system field?

[Anonymous]

Here are the system fields when I click on the first field it goes to second position and so on is not fixed.

the second figure is the global histogram of all the fields and I would like to click for example on #Satisfaction_client and display its histogram only.

thank you for your reactions.

[t_chetirbok]

Hi Franck,

we need to see your dimensions/ expressions in the chart

[Anonymous]

Tatsiana the  dimension is ( mois)

and the expression is Avg(#taux_protection_antivirus_mois) in the case of one only field.