Suppose there are two car manufacturing company, which produces two different cars.The number of cars manufactured monthly is,
→Company A →→→→40 40 50 60 60 70 80 90 50 30 120 200
→Company B→→→→→20 30 40 50 60 80 80 100 100 120 140 180
So, if 10 cars manufactured is represented by symbol →Δ
Company A→→ΔΔΔΔ ΔΔΔΔ ΔΔΔΔΔ ΔΔΔΔΔΔ ΔΔΔΔΔΔ ΔΔΔΔΔΔΔ ΔΔΔΔΔΔΔΔ ΔΔΔΔΔΔΔΔΔ ΔΔΔΔΔ ΔΔΔ ΔΔΔΔΔΔΔΔΔΔΔΔ ΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔ
Company B→→ΔΔ ΔΔΔ ΔΔΔΔ ΔΔΔΔΔ ΔΔΔΔΔΔ ΔΔΔΔΔΔΔΔ ΔΔΔΔΔΔΔΔ ΔΔΔΔΔΔΔΔΔΔ ΔΔΔΔΔΔΔΔΔΔ ΔΔΔΔΔΔΔΔΔΔΔΔ ΔΔΔΔΔΔΔΔΔΔΔΔΔΔ ΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔΔ
By looking at the Symbols we can compare easily, which company has manufactured more cars if we have represented through tally marks.
By looking at the pictures answering becomes easier.
Now, a days tally marks is used , but if data values are high, we use symbols, so our work that is representation of thing becomes easier on the graph.