Overlaying visual interface information atop a video signal without obscuring desired features of the video signal. In particular elevated pressure is maintained to prevent alcohol boil off during initial mixing and reaction of the reactants prior to any catalyst addition, and preferably the pressure is reduced rapidly after the desired reaction temperature has been reached. Since the output of the bridge circuit is in proportion to the difference in electrical resistance values between the first and second elements, part of a change due to causes other than the magnetic field is canceled in the output of the bridge circuit, whereby the magnetic field value can be accurately measured. The hit ratio may be computed as the ratio of the sum of the actual excess returns to the sum of the total available excess returns for each call by the analyst over the call evaluation period.