Why were strain gages first produced with 120 Ω resistance?

According to Frank Tatnall in his book "Tatnall on Testing" (1966, American Society of Metals, p. 101) and as reported in the “SR-4 News Letter” (1940s):

“A gage resistance of 120 ohms was selected first, because it would pass 25 milliamperes in a bridge circuit at 6 volts.  Second, this resistance is large compared to the 6.385 ohms per 1000 feet of the 18 B and S gage copper leadwires, and third, 120 ohms is sufficient great enough to avoid being too badly affected by switching resistance using silver-tipped switches, yet 120 ohms is small enough so that only a 5-inch length of 1-mil copper-nickel wire need be used to attain this resistance value.”

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Gregg Cockroft

Technical Sales Manager