A test member suitable for use in a test device for testing of analyte concentration in a fluid to be applied thereto comprises a base member having a working area to which the fluid is to be applied, containing a reagent which is reactive to the said analyte to produce an electrical signal or a color change, and a non-working area adjacent to the working area. When the controller device gets a GUID from a target device after bus reset, the controller device searches for a record of the target device corresponding to the gotten GUID from the records in the current function information list and the past function information list prior to the bus reset. The processing means is further arranged to calculate a maximum value of the mean square displacement <rm2 from the autocorrelation function g as a function of time and the value of the property from said calculated maximum value of the mean square displacement rm2.