Sound velocity varies as a function of pressure, temperature and salinity.   Most open ocean conditions see sound velocities of between 1400 and 1550 metres per second.  That said, under extreme conditions of temperature - for example, in the Persian Gulf - or depth - for example, in the Marianas Trench - sound velocities may move beyond this standard range.  The graph below depicts environmental conditions and their corresponding sound velocity ranges.  

Extreme salinity can also alter sound velocity.  For example, sound velocities in the Dead Sea of Israel or in Great Salt Lake of Utah, America can range as high as qrs.  Another example would be underwater caverns containing salt water brine, where again sound velocity can rise as high as 1850 m/s. 

Many vendors of oceanographic instrumentation refer to accuracy and precision interchangeably.  They are not interchangeable.  In effect, accuracy refers to how well a sensor performs against a known third party standard.  For example, a temperature sensor may be +/- 0.001 C, as compared to a Black Stack themistor module.  Precision refers to the repeatability of the readings of a given sensor.   A sensor is precise when it repeatedly provides the same reading, regardless of how accurate that reading is.

A good analogy is a dart board.  The thrower of darts is accurate when he or she is able to reach the target, the bulls-eye.  He or she is precise if, having thrown three darts, all three land in the same location, irrespective of whether or not that location is the bulls-eye.