The Z562M3 is a special nixie tube manufactured by WF / RFT. It can display two arrows. It was used in elevators to indicate "going up" and "going down", but it also could be used for indicate left and right. There is also another tube, the Z562M2, that was used in elevators, it can display 1-8,E,K for indication of floors. A Z562M1 also exists, but this was not made for elevators, it can display X,Y,Z,R symbols for coordinates. This tube is very rare, i believe not many of them were made at all.