The final step of preparation for the evaluation is to process the reference annotation files to obtain reference heart rate annotation files. These files must contain heart rate measurement annotations with the same measurement numbers assigned as for the test heart rate annotations; they need not necessarily contain beat or other annotations from the reference annotation files. Quoting from EC38,
To evaluate the accuracy of heart rate measurement, the evaluator shall implement and disclose a method for obtaining heart rate measurements using the reference annotation files (the `reference heart rate'). This method need not be identical to the method used by the device under test, but in general it will be advantageous if it matches that method as closely as possible.It will generally be in the manufacturer's interest to provide a program for generating reference heart rate annotation files, to avoid the need for an independent evaluator to do so, with a likely result of less than optimal agreement with the test heart rate measurements. The DB software package includes a sample implementation of such a program (examples/refhr.c); note that it will need to be customized for each device to be tested.
Note that measurement errors are normalized by the mean value of the reference
measurements in each record. Be certain that this mean value cannot be
zero!