The 529 number denotes European water standard tolerances and specifications for water damage. All electrical devices inspected by the IEC have a 529 designation. This is similar to MIL-STD 810 (military standard 810) in the United States. The second set of numbers define what category the device falls under. For example, the IPX0 has no water protection.
The number after the IPX denotes what level of protection is afforded against water. The scale ranges from IPX0 to IPX8. The first standard, zero, means the device has no water protection. Eight means the device is fully submersible, like a scuba diver's watch or depth gauge. IPX7 means the device is submersible for 30 minutes maximum, for no deeper than one meter without suffering water damage. A meter is about 39 inches, or a little bit longer than a yard. If the device is submerged for longer than 30 minutes, it will suffer damage, or if the device is brought deeper than 1 meter, it will suffer damage.
The IPX defines the outer case construction. IP stands for "Immersion Protection." The X is a place marker. If you see an X, it means the device has no special heavy duty case to guard against being hit or falling.
Putting it all together, The IEC 529 IPX7 standard defines the entire device. First, the 529 states it was water tested. Second, the IPX states the device has no special cladding or armor to guard against hits or drops. Third, the 7 states the device can be submersed to 1 meter maximum depth or 30 minutes maximum time without sustaining water damage.