A method and apparatus for determining on-machine, components of variances over an entire frequency range, of a property of a substantially continuous moving sheet material. At least two property-sensing detectors measure and each provide a signal Y(t) proportional to a sheet material property at a different...http://www.google.de/patents/US4910688?utm_source=gb-gplus-sharePatent US4910688 - On-machine sheet material property analysis
