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Most of these types of devices used nickel-chromium wire wound on ceramic forms.
These values show how much resistance is to be subtracted if the junction is shunted by a pin.Various types of laboratories also purchased L & N equipment.L&N was a major supplier of various types of devices that were used for industrial calibration of temperature sensors and associated temperature monitoring instruments.Today there is a Leeds & Northrup doing business out of the UK specializing in industrial furnace temperature monitoring devices. One of Edward Weston's products was "The Weston Standard Cell" which was a mercury-cadmium battery that provided a very specific DC voltage that didn't change over long periods of time. Cell voltage was nominally 1.018638vdc for most of its life.A Standard Cell provided a reference voltage for calculation of various circuit values or a specific voltage supplied for precision measurement type comparisons.These would be thermocouples, RTDs and other temperature sensors or transducers.
L&N built precision resistance devices including decade boxes, various types of elaborate potentiometers, fixed resistances along with sensitive galvanometers, individual component-type Wheatstone Bridges and many other types of instruments.
These types of boxes were used in DC Resistance bridge circuits for precise measurements of an unknown resistance (Wheatstone Bridge circuits) or in other circuits for calculating current flow, low voltage levels or comparison evaluations.
Both of these Otto Wolff resistance boxes were used a Mount Wilson Observatory in Southern California. Wilson and the facility there had (has) a lot of very early test gear.
I was given these boxes by my old Virginia City friend, Maynard Clark who worked at Mount Wilson Observatory (Maynard designed much of the computer software for the various telescope drive systems at Mt.
Wilson.) These large, adjustable wire-wound rheostat-potentiometers were generally used in college and university physics laboratories when performing experiments in electricity where fairly large currents were involved.
Laboratory R-C-L Devices, Diagometers & Test Kits, RF Signal Generators, Freq Measuring Instruments, AF Oscillators, Voltage Measuring Instruments, C-L-R-Z-Q Measuring Instruments, Vacuum Tube Testers, Oscilloscopes, Panadapters, Xmtr Modulation Monitors, Digital V & F Measuring Instruments, Test Bench Power Supplies, Variable Voltage Xmfrs, Miscellaneous Instruments Test instruments that are built to a high-quality standard are generally referred to as "Laboratory Equipment." Some of the test equipment used in early laboratories may seem archaic and useless today but their purpose and operation is interesting and historically important.