1491 Series INDUCTOR DECADE BOX

1491 Series Decade Inductor is the same as GenRad inductor decade. 
The 1491 Decade Inductor is an assembly of several Decade-Inductor Units in a single metal cabinet. The units have no electrical connection to the panel, but a separate ground terminal is provided, which can be connected to the adjacent low terminal, leading to the smallest decade.

• Shielded toroidal cores for small mutual
  inductance and minimal effect from external
  fields

• Sealed against moisture for long term stability

• Excellent as a moderately precise standard
  of inductance .

• High-Q, 200 and above

These inductance decades are convenient elements for use in wave filters, equalizers,
and tuned circuits throughout the range of audio and low radio frequencies.
As components in oscillators, analyzers, and similar equipment, they are especially
useful during the preliminary design period, when you need to vary circuit elements
over relatively wide ranges to determine optimum operating values. 
As moderately precise standards of inductance they have values of low-frequency storage factor, Q, that are much larger than those of air-core coils.