Waterproof Level of electronic measuring instruments reflects their freedom from dampness and dusts at the same time. It is unavoidable for them to be exposed to heavy dampness and terrible dusty environments, especially when they are used in the open air. The capability of an instrument to be free from water or damp air is of vital importance to the normal operation and lifespan of the instrument. Therefore, the standard of IEC529 was established and is well recognized throughout the world. To be in consistence with the Standard, the Japanese Industrial Standard divided waterproof protection into ten levels, identified as IPX1, IPX2...respectively.
What the TEN Levels mean is as follows:

0. Without protection
1. Protection against water drops from vertically above, free from negative influences.
2. Protection against water drops that come from within a 15-degree area from the vertical direction, free from negative influences.
3. Protection against rain coming from within a 60-degree area from the vertical direction, free from negative influences.
4. Protection against water splash from any directions, free from negative influences.
5. Protection against direct water spray from any directions, free from negative influences.
6. Protection against direct water spray from any directions, preventing water from getting into the inside of an instrument.
7. Protection against soaking in water, preventing water from totally entering into the inside of an instrument under certain conditions.
8. Enabling normal use after being soaked in water under certain pressure for a long time. 
9. Enabling normal use under circumstances where comparative humidity is less than 90%.