The National Weather Service (NWS) periodically conducts sensor comparison studies to ensure that proposed observing equipment meets requirements set forth in specific solicitations. Other comparison studies may occasionally be conducted in support of a specific project or request, the requirements for which provide the evaluation criteria. The final result of these studies, along with the test data, is usually a summary report documenting the suitability and performance of the selected sensor(s) based on criteria established in the acquisition specification. In the case of studies in support of an acquisition, a sensor evaluation study usually involves three phases. Two of these, the initial laboratory testing and the controlled environment testing, may include vendor-proprietary or other data related to acquisition decisions, and so the results of that testing are not archived. A final phase of testing is the characterization study, usually conducted at the NWS Sterling Research and Development Centers located in Sterling, VA. A characterization study typically spans a year or more, and involves a group of comparison sensors. This study includes test data and supporting documentation from the Sutron Fischer and Porter Rebuild (FPR) kit characterization study at the Sterling Field Support Center in 2008 and 2009. The primary objective of this test was to determine if the accuracy and overall functionality of the Sutron FPR kits met the requirements of the QPL specification (Specification NWS-D111-5-SP001, Fisher and Porter/Belfort Precipitation Gauge Rebuild Kit) over a period of one year. This was accomplished by analyzing sensor drift through calibration, conducting exposure tests, and performing a field demonstration to determine if the Sutron kits met QPL requirements. The study compared the FPR kits with the current version F&P gauges and an ASOS All Weather Precipitation Accumulation Gauge (AWPAG) in a 12-meter Double Fence Intercomparison Reference (DFIR). The long term specification compliance testing shows that the Sutron FPR kits installed in the field met the NWS-D111-5-SP001 specifications.