The ZM1041 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 measurement instruments. According to tesla's datasheet a clear-glass editon, the ZM1043, also exists. There is also a different version, the ZM1041S, with additional Symbols