The ZM1041S is a special character indicator tube with red coating for better contrast. The character height of 30mm makes this tube a companion to numerical indicators like the ZM1040. Its a rare tube, beause it was produced in less numbers as the numerical indicators. I assume these tubes were used in applications where positions are envolved (X-Y-Z axis) or in measurement instruments. According to tesla's datasheet a clear-glass editon, the ZM1043S, also exists.