Refer to figure.
Since the table does not provide percentage of brake horsepower (% BHP) at 5000 ft, the values at 4000 ft and 6000 ft must first be obtained and then interpolated to determine the % BHP at 5000 ft.
Step 1: Find the % BHP at 4000 ft

1. Enter the table at a pressure altitude of 4000 ft.
2. Move across to 2500 RPM.
3. Read the corresponding % BHP of 74% from the right column.

Step 2: Find the % BHP at 6000 ft

1. Enter the table at a pressure altitude of 6000 ft.
2. Move across to 2500 RPM.
3. Read the corresponding % BHP of 70% from the right column.

Step 3: Calculate the % BHP at 5000 ft
Since 5000 ft lies midway between 4000 ft and 6000 ft, the average of the two values can be taken.

• % BHP at 5000 ft = (% BHP  at 4000 ft + % BHP at 6000 ft) / 2
• % BHP at 5000 ft = 74% + 70% / 2
• % BHP at 5000 ft = 72%