Which turn-and-slip indicator shows a standard-rate turn of three degrees per second?

The standard rate turn indicator is designed to show when an aircraft is performing a turn at the standard rate, which is defined as a turn of three degrees per second. This is an essential reference for pilots as it helps ensure that turns are made within controlled parameters, which is particularly important in instrument flight operations. Maintaining a standard rate turn is crucial for avoiding excessive bank angles and ensuring spatial awareness, especially in conditions where visual references are limited.

In contrast, the other terms do not accurately describe the instrument used for indicating turns in degrees per second or do not exist in standard aviation terminology. The concept of a "redundant power indicator," "standard turn indicator," or "three-degree turn indicator" does not align with the instruments commonly used in aviation to measure turn rates. Hence, the standard rate turn indicator is the correct instrument for showing the established standard rate of turn for aircraft.