Waterproofness is measured using something called an ‘ingress protection standard’, which is published by the International Electrotechnical Commission. In effect, it standardises the testing and measurement of devices, so that a product can be given an objective rating of the protection it has built in. The higher the rating, the more protection you get from ingress. Once tested, there are two digits given to an IP rating. For example, “IP54”. The first digit is a measure of protection from intrusion of solid objects (rated 1-6), and the second is a measure of protection from moisture (rated 1-9).Basic definitions for the moisture protection ratings can be found in this IP rating table: x/0 - Not rated 1 - Protection against vertically falling droplets, such as condensation. 2 - Protection against falling water droplets deflected up to 15° from vertical. 3 - Protection against moisture spray up to 60° from vertical. 4 - Protection against water splashes from all directions. Tested for a minimum of 10 minutes with an oscillating spray (limited ingress permitted with no harmful effects). 5 - Protection against low-pressure jets (6.3mm) of directed water from any angle (limited ingress permitted with no harmful effects). 6 - Protection against high-pressure jets (12.5mm) of directed water from any angle. 7 - Protection against full immersion for up to 30 minutes at depths between 15cm and 1m (limited ingress permitted with no harmful effects). 8 - Protection against extended immersion at greater depths. Precise parameters of this test are set and advertised by the manufacturer and may include additional factors such as temperature fluctuations and flow rates, depending on equipment type. 9K - Protection against high-pressure, high-temperature jet sprays, wash-downs or steam-cleaning procedures. So, an IP54 rating means a device has been tested and rated for protection against water splashes in all directions (the ‘5’ actually has nothing to do with moisture – this is its separate protection rating for solid object intrusion).Note: an ‘x’ or ‘0’ rating (e.g. IP6x or IP60) indicates that no rating has been given for that measure.