Multiple signals are monitored, for example, by an instrument used for monitoring wavelength division multiplexing transmission systems. In one example, A quick disconnect valve assembly includes first and second valve elements configured to releasably engage each other. The first pixel rows read R, G, B color components of a document image while scanning the document in a main scanning direction. The delay timing and signal change are used to calibrate the various channels of the tester. The generated transaction acoustic signal is electronically transferred to an end device, which processes the selected transaction data only when the user of the data carrier confirms vis-\xe0-vis the end device an at least partial match both of the acoustically reproduced melody with the user-specific melody and of the acoustically reproduced transaction data with the selected transaction data.