charts with new variable
 

Hi! I want to create a chart to show the evolution of the mass of a component in a room (Mass of the component - Time). I can obtain the mass for each step with the function volumeInt in the Function Calculator but the menu of the chart asks me for an expression. What should I write there? I've tried with:

volumeInt (Product)

where Product makes reference to the density of this component. But it hasn't worked. Creating an expression with the same hasn't worked either. Does someone know why? Thank you!!