The major lines you read on the y-axis (vertical axis) are minutes. The minor lines are quarters of minutes. Starting from 0, the first dotted line would be 15 seconds, then 30 seconds for second line, 45 seconds for the third line, and then 1 minute for the next solid line. The major lines you read on the x-axis (horizontal axis) are in kilometers. Each major line is 500 km. Each dotted line is 250 km.