The terms top forty/pop CHR (contemporary hit radio) and Rhythmic CHR are probably only meaningful to program directors and record company executives, but the differences are discernible in a major market. Pop/CHR stations attempt to a synthesize the best elements of rock and rythym and blues. Rhythmic/CHR stations focus on rythym and blues, hip hop and dance (i.e. songs played in clubs). As in the discotheques of the early '60s, today's club scene remains an ideal testing ground to measure the visceral effects of the latest releases. Some club DJs move on to lucrative radio careers as "mix masters," recreating their best sets of dance tunes on the air.