  The Bent Crystal Spectrometer (BCS) onboard the NASA Solar Maximum Mission
was part of the X-ray Polychromator, which observed numerous flares and bright
active regions from February to November 1980, when operation was suspended as
a result of the failure of the spacecraft fine pointing system. Observations
resumed following the Space Shuttle SMM Repair Mission in April 1984 and
continued until November 1989. BCS spectra have been widely used in the past to
obtain temperatures, emission measures, and turbulent and bulk flows during
flares, as well as element abundances. Instrumental details including
calibration factors not previously published are given here, and the in-orbit
performance of the BCS is evaluated. Some significant changes during the
mission are described, and recommendations for future instrumentation are made.
Using improved estimates for the instrument parameters and operational limits,
it is now possible to obtain de-convolved, calibrated spectra that show finer
detail than before, providing the means to improved interpretation of the
physics of the emitting plasmas. The results indicate how historical, archived
data can be re-used to obtain enhanced and new, scientifically valuable
results.
