The original fit of Rad Alt on all Shacks was Rad Alt Mk5.
This had an indicator, height selector and the three “traffic” lights to indicate postiton relative to the selected height. (These can clearly be seen on the panel, lower right) Having been the “Rad Alt 5” expert for a while at St.M I can tell you that it was inaccurate and very unreliable! A number of new fits were tried, some retaining the traffic lights, the MKIII finally had the superb Honeywell version that went on to be fitted in a number of airframes. (The Nimrod had a dual fit). It was so accurate that you could see the difference when the aircraft was jacked up.