Operating a CH station was a manpower-intensive situation, with an operator in the transmitter hut, an operator and assistant in the receiver hut, and as many as six assistants in the receiver hut operating the plotters, calculators and telephone systems.
In order to provide 24-hour service, multiple crews were needed, along with a number of service and support personnel.
This was then multiplied by the reporting hierarchy, which required similar numbers of WAAFs at each level of the Dowding system hierarchy.

Plotting the angle of the target was a simple process of taking the gonio reading and setting a rotating straightedge to that value.
The problem was determining where along that straightedge the target lay; the radar measured the slant range straight-line distance to the target, not the distance over the ground.
That distance was affected by the target's altitude, which had to be determined by taking the somewhat time-consuming altitude measurements.
Additionally, that altitude was affected by the range, due to the curvature of the Earth, as well as any imperfections in the local environment, which caused the lobes to have different measurements depending on the target angle.

As no small part of the manpower required was dedicated to calculation and plotting, a great reduction could be made by using as much automation as possible.
This started with the use of various mechanical aids; these were eventually replaced by the fruit machine, an electromechanical analogue computer of some complexity.
It replicated all of these devices and tables in electrical form.
An electrical repeater, or synchro, was added to the gonio dial.
To measure the range, a new dial was added that moved a mechanical marker to a selected blip on the display.
When a particular target was properly selected, the operator pushed a button to activate the fruit machine, which then read these inputs.
In addition to the inputs, the fruit machine also had a series of local corrections for both angle and altitude, as measured by calibration flights and stored in the machine in telephone uniselectors.
These corrections were automatically added to the calculation, eliminating the time-consuming lookup of these numbers from tables.
The output was the altitude, which then allowed the plotters to determine the proper over-ground distance to the target.

Later versions of the fruit machine were upgraded to directly output the position of the aircraft with no manual operation.
Using the same buttons to send settings to the machine, the operator simply triggered the system and the outputs were used to drive a T-square-like indicator on the chart, allowing the operator to read the calculated location directly.
This reduced the number of people needed at the station and allowed the station to be reorganized into a much more compact form.
No longer did the operator call readings out to the plotters; now they sat directly beside the plotting table so they could see if the results looked right, while the tellers could see the plot and call it into the area plotting room.
A further upgrade allowed the data to be sent to the local plotting room automatically over the phone lines, further reducing the required manpower.
Operating a CH station was a manpower-intensive situation, with an operator in the transmitter hut, an operator and assistant in the receiver hut, and as many as six assistants in the receiver hut operating the plotters, calculators and telephone systems. In order to provide 24-hour service, multiple crews were needed, along with a number of service and support personnel. This was then multiplied by the reporting hierarchy, which required similar numbers of WAAFs at each level of the Dowding system hierarchy.
Plotting the angle of the target was a simple process of taking the gonio reading and setting a rotating straightedge to that value. The problem was determining where along that straightedge the target lay; the radar measured the slant range straight-line distance to the target, not the distance over the ground. That distance was affected by the target's altitude, which had to be determined by taking the somewhat time-consuming altitude measurements. Additionally, that altitude was affected by the range, due to the curvature of the Earth, as well as any imperfections in the local environment, which caused the lobes to have different measurements depending on the target angle.
As no small part of the manpower required was dedicated to calculation and plotting, a great reduction could be made by using as much automation as possible. This started with the use of various mechanical aids; these were eventually replaced by the fruit machine, an electromechanical analogue computer of some complexity. It replicated all of these devices and tables in electrical form. An electrical repeater, or synchro, was added to the gonio dial. To measure the range, a new dial was added that moved a mechanical marker to a selected blip on the display. When a particular target was properly selected, the operator pushed a button to activate the fruit machine, which then read these inputs. In addition to the inputs, the fruit machine also had a series of local corrections for both angle and altitude, as measured by calibration flights and stored in the machine in telephone uniselectors. These corrections were automatically added to the calculation, eliminating the time-consuming lookup of these numbers from tables. The output was the altitude, which then allowed the plotters to determine the proper over-ground distance to the target.
Later versions of the fruit machine were upgraded to directly output the position of the aircraft with no manual operation. Using the same buttons to send settings to the machine, the operator simply triggered the system and the outputs were used to drive a T-square-like indicator on the chart, allowing the operator to read the calculated location directly. This reduced the number of people needed at the station and allowed the station to be reorganized into a much more compact form. No longer did the operator call readings out to the plotters; now they sat directly beside the plotting table so they could see if the results looked right, while the tellers could see the plot and call it into the area plotting room. A further upgrade allowed the data to be sent to the local plotting room automatically over the phone lines, further reducing the required manpower.
Chain Home