88 before decision boundaries are crossed for example fig3 illustrates decision boundaries 75 for 64 qam overlaid onto the 16 qam symbol decision grid for an exemplary 16 qam symbol value 55 n as can be clearly seen same magnitude of the symbol displacement 88 that may not cause a cwe on a packet modulated at 16 qam will cause a cwe if the packet were to be modulated at 64 qam accordingly another aspect of the present invention provides a method of estimating a projected network performance after switching from a first modulation format to a second modulation format based on measurements done only for the first modulation format by way of example only embodiments described hereinbelow may be described with reference to 16 qam as the first modulation format and 64 qam as the second modulation format although the present invention is not limited thereto with reference to fig4 one embodiment of the present invention provides a network tester 100 that is capable of such predictive testing the tester 100 which can be used to embody the stationary testing equipment 18 and or the portable tester 19 includes a receiver unit 205 such as the front end receiver tuner 310 of the cm rx 300 which connects to a measurement processor mp 200 that is configured to provide predictive symbol based and codeword based metrics a measurement controller mc 270 may also be provided for performing the measurement control and result aggregation functions such as those described hereinabove with reference to the measurement controller 303 as well as additional score generating functions described.