RAJAR, the new joint industry measurement system for UK radio, was launched in 1993. As in the past, the RAJAR survey uses a one-week self-completion diary and a model is required to estimate station or schedule reach beyond seven days. Changes in the radio market have led to changes in listening habits and a consequent need to update the extended reach model. The new model is probability based and has been validated using a one-off four week diary study. The published station reach build curves are used by several bureaux as a basis for providing the advertising industry with a practical system for schedule reach and frequency analysis. Two bureaux - IMS and Telmar - collaborated to ensure consistency in their approach to the estimation of schedule reach. However, each system offers several ways in which the base data can be used, essentially depending upon whether a schedule is being planned in broad time segments or using exact spots. These permutations are seen to generate greater inconsistencies in estimates of frequency rather than reach. Without an understanding of how each bureaux system will interpret an analysis specification, buyers and sellers of airtime could well be negotiating with inconsistent and misleading reach and frequency results.