Before the publication of the ISO 3383-3 standard for measurements in open plan offices,
the system calibration was only used for the measurement of the Strength (G) parameter,
and related parameters such as the early and late strength (G80 and GL),
and the lateral sound levels (GEL and LG).
Since the introduction of ISO 3382-3, the use of system calibrations has increased significantly.
Performing an accurate system calibration can be a challenging task.
For the best results, an anechoic room or reverberation chamber is required,
and even there it is difficult to get results with an error margin close to 1 dB.
Not everyone has easy access to an anechoic room or a reverberation chamber,
and therefore the in-situ free-field system calibration method is often used.
The following are three important concerns with this type of calibration.