Takeoff quantities come in three kinds: counts, lengths and areas. Counts apply to items priced by the piece.
An electrician counts receptacles by type on each floor plan. A gym equipment contractor counts backstops, volleyball sleeves and wall pads.
Count by symbol and check the legend first. Mark each symbol as you go. Then compare your total with the schedule.
When the plan count and the schedule differ, note both numbers. Send an RFI or qualify which one you priced.