This video shows how to use a peak flow meter, and discusses the 20% diurnal variation which is looked for as part of diagnosing asthma in someone above the age of 17. A peak flow meter is a portable, easy-to-use tool that measures how well your lungs are functioning, by allowing comparison of the speed at which you can exhale - your peak expiratory flow rate (PEFR) - in Litres per minute Your PEFR is compared against your predicted PEFR based on your height, age and sex which all allow you to determine how well your asthma is controlled. The video will look not only at how to use a peak flow meter, but also how to use a Respitmat, Salbutamol MDI and Elipta inhalers