Sansui followed a long established tradition in the early to mid century radio/electronics world of offering models on a numbering system where the first digit if low, 1 to 3 (but never Zero) was an entry level set. Numbers beginning with 4, 5 and 6 were mid level, and the top offerings had the 7, 8 and 9 digits. Market coverage and manufacturing logistics worked as counter-balancing forces. If a line could not be offered in nine different levels, the skipped digits were often those which were considered less preferred or less lucky. 7 is a lucky number in Japan, and anything top level would begin with 9. So 6 was often skipped, and 5 being mid-level market was often used. If a series was released without low number prefixes it was not intended to have components offered in the entry level market. Most manufacturers followed this general idea. One major company, Marantz, seemed to use a different system where the first digit was a code for the type of equipment.
The super ultra sets by Sansui with five digits: Although they began with 1s 2s and 3s they were obviously not "Entry Level" machines. But they did come later.
