My fault.
737CL has only a asymmetry funktion and the 737NG in addition has a flap skew funtion.
737CL :
The flap position indication comes
direct from the two flap position transmitters.
Inside of the flap position Indicator is a comparator switch.
He compares the position of both pointers. When the two pointers separate by a predetermined amount the comparator switch closes and applies power to the asymmetry shutoff relay. The energized relay drives the trailing edge flap bypass valve to bypass and stops the hydraulic motor.
So the pointers show the real position.
737NG:
The flap position indication comes from the FSEU which gets his information from the two flap position transmitters.
The FSEU compares the data from the left and right TE flap position transmitters to monitor the position of the TE flaps.
If they are different by more than 9 resolver degrees, there is an asymmetry condition and the FSEU operates the bypass valve.
During an
asymmetry condition, the needles on the flap position indicator show the actual data from the flap position transmitters.
But in addition you have 8 flap skew sensors (one at each transmission).
The FSEU use the values from the flap skew sensors to prevent skew.
The FSEU compares skew sensor 1 with 8, 2 with 7, 3 with 6 and 4 with 5.
If a predetermined value is exceeded the FSEU operates the bypass valve.
The FSEU compares the skew sensor on the skewed wing to the flap position transmitter. If the skew sensor position is more than the position transmitter position, the FSEU makes the needle for the skewed flap move 15 degrees in the extend direction. If the skew sensor position is less than the position transmitter position, the FSEU makes the needle for the skewed flap move 15 degrees in the retract direction.
It is important to anderstand that the indication on a 737CL is direct and on a 737NG the indication is generated by the FSEU.