This is the way to look at the amount of acid entering the lower part of the oesophagus which might cause problems due to reflux. It is a thin plastic tube placed usually at endoscopy so the insertion does not cause any discomfort and the tip lies about 3-4 cm above the junction of the oesophagus and the stomach. It is attached to a small box the size of a iPod type device and is usually left for 24 hours and the infant or child is encouraged to have as normal a day as possible. It records the amount of acid entering the oesophagus and this information can then be downloaded onto a computer and event markers such as sleeping, feeding and discomfort experienced can be recorded and then used in conjunction with the acid trace on the computer to determine the importance of any acid reflux causing problems and to determine the extent and severity of the gastro-oesophageal present.