To establish your best peak expiratory flow reading, you should measure:

Measuring peak expiratory flow readings twice daily for 2-3 weeks without symptoms is the best approach to establish a reliable baseline for an individual's peak flow. This method allows for a comprehensive assessment of lung function over time, accounting for normal variations that can occur due to factors like time of day, physical activity, and environmental conditions.

By taking measurements twice daily, one can capture the variability in lung function that may not be apparent with less frequent assessments. A duration of 2-3 weeks helps to average out any anomalies that might occur, allowing for a more accurate depiction of the person's typical peak expiratory flow. This extended period of monitoring without symptoms ensures that the readings reflect the individual's baseline lung function rather than responses to acute illness or exacerbations.

In contrast, taking readings less frequently or for shorter durations may not provide sufficient data to determine an accurate baseline or could lead to misleading conclusions about respiratory health.