Refer to figure.
EASA learning objective 022.04.02.01.07 states: 'Describe the indications given by a turn coordinator (or turn-and-bank indicator)'.
EASA learning objective 022.04.02.01.02 states: 'Define a ‘rate-1 turn’.'

The turn coordinator is a gyroscopic instrument designed to indicate an aircrafts rate and direction of turn, it also incorporates a balance indicator to enable pilots to fly balanced turns.

The turn coordinator is a variation of the turn indicator, its horizontal gyro being inclined at 30° to make it sensitive to roll as well as yaw. Despite roll causing movement of the aircraft symbol the turn coordinator does not measure rate of roll, angle of bank or give any pitch information.

Air Traffic procedures require a predictable aircraft rate of turn for instrument approaches and holding procedures, this standard rate of turn is called 'Rate 1'.

A 'Rate 1 Turn' is a turn rate of 3 degrees per second or 360 degrees in 2 minutes. The turn coordinator has calibration markings to indicate a rate 1 turn.

Although the turn coordinator incorporates a balance indicator (slip ball), this is a separate instrument which enables the pilot to fly a balanced turn. The primary function of the turn coordinator is to indicate direction and rate of turn.