Under what condition does indicated altitude equal true altitude?

Indicated altitude equals true altitude when an aircraft is at sea level under standard conditions, which refer to a temperature of 15 degrees Celsius (59 degrees Fahrenheit) at sea level and a pressure of 29.92 inches of mercury. Under these precise conditions, the relationship between pressure and altitude is aligned perfectly, allowing the indicated altitude shown on the altimeter to accurately reflect the actual height above sea level.

In other scenarios, such as flying below 10,000 feet, atmospheric variations, temperature differences, or miscalibrated altimeters can cause discrepancies between indicated altitude and true altitude. During a climb, the altimeter will display changes in indicated altitude that may not correspond with true altitude due to changing atmospheric pressure. Additionally, while flying at an altimeter setting of 30.00 inches of mercury, the indicated altitude could still differ from true altitude depending on the overall atmospheric conditions and elevation.