Capacity is the time a person can work in the period you are planning. Start with their contracted weekly hours and subtract leave recorded for that week. A part-time colleague's denominator is their own working pattern. You can't replace it with a standard forty-hour week and still compare people fairly.
Desk Staffing stores hours by Monday-starting week. Read the week on the capacity view before calculating. Leave in the following week doesn't reduce this week's supply. A full week of leave gives zero capacity, so the person can't take a booking that week. The fictional records include part-time staff and leave so you can check these boundaries before scheduling client work. Report net hours first; utilization comes after you know the denominator.