The visible channel of the Imager instrument onboard the Geostationary Operational Environmental Satellite (GOES) is not absolutely calibrated once launched. For many purposes, it is crucial to understand the characteristics of instrument degradation with time. A recent study by Knapp and Vonder Haar (JAOT 2000) confirms the results we obtained during the GOES-11 Post-Launch Science test. The close agreement is remarkable for several reasons. (1) They relied on a radiative transfer model, whereas our approach is largely empirical. (2) They restricted their study to the dark ocean scene only, whereas we examined scenes for a wide range of illuminations. (3) They studied GOES-8 only, whereas we studied both GOES-8/10. The implications of the similarity in results, despite the differences cited, will be discussed. Results from GOES-11 will also be shown.