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To select a R value one first has to know the total resistance of the box.
In the case of the Central Scientific box shown, the total R is 1100 ohms.
Otto Wolff, from 1900 to 1909, produced the Reichsanstalt-type of resistance standards used at the National Bureau of Standards (NBS.) At the turn of the last century, many precision measurements had to be calculated because the measurement couldn't be made directly since many of the instruments we take for granted today hadn't been developed.
A known precision resistance allowed one part of the equation to be selected and the remainder was then calculated.
Most of these types of devices used nickel-chromium wire wound on ceramic forms.
The following is a sample of some of the very best laboratory-quality vintage test instruments along with some of the most elaborate (expensive) military test gear and also some service test equipment from the other end of the price spectrum - H.
Rogers Nov, 2014 These two precision resistance boxes were built in Berlin by Otto Wolff and date from around 1900. Biddle of Philadelphia imported these instruments and each box has his tag attached.