Zero
Ok you win! Your quote is just about there. However you're confusing the compressors with the compressed gas. As your quote says, surging is the complete breakdown of flow and compression, caused, generally, by the compressor blades losing 'lift' and stalling. This can happen for any number of reasons, which, as before, you can search for. This 'stagnation' in flow results in the, relatively, HIGH PRESSURE gas, downstream of the area of stall reversing flow into the LOWER PRESSURE area, forward. This is generally quite a violent action, causing the engine to pop, bang and fart, sometimes with disastrous results. The crew will hear and feel this, along with yawing, especially in a twin, due to the loss of thrust, but they'll also get indications on their instruments, such as a rise in TGT, RPM changes and, if used, EPR changes.
The problem with 'Sad Sams' explanation is that he obviously doesn't know how the engine works! Those who know how a gas turbine works could see the error immediately. The gas is constantly being pressurized through the compressor so that, at any given point, the pressure is s set value, ish (again, lots of variables. Google 'Gas Turbine Theory'
So, completely the the wrong end of the stick! As I said, anybody with a basic grasp of schoolboy physics would be able to tell you that a low pressure gas CANNOT flow into a high pressure one.
There now....satisfied