??mm symbol tube manufactured by National Electronics

The NL-864 is a clear glass symbol tube made by National Electronics. There is one symbol row with "Hz, S," and on top a second row with "K,µ,n,M", making it possible to display "kHz". I guess this tube was used in a frequency counter or similar device. Currently i have no more info about this tube or any data. It seems to be a rather rare tube.
Brand / Manfacturer National Electronics
Same Types
Likely Tyes
Symbol height in mm ??
Characters / Symbols Hz,S,K,µ,M,n
Decimal point none
Base / Socket 0
Starting Voltage (typ) 0 V
Maintaining Voltage (typ) 0 V
Current per Segment 0mA
Reccomend Resistor 0