of the motor-driven units was observed; current practice is to provide adequate temperature insulation.
(4) Barograph
As a secondary pressure unit, a clock-driven barograph has been included on many flights. The instrument (shown in Figure 33)
Figure 33. Smoked drum barograph.
will provide up to 40 hours of pressure data if recovered. About 70% of all those units flown to date have been recovered. The performance specifications are as follows:
(a) Rotation: one revolution every 12 hours
(b) Duration: 36 hours running time
(c) Pressure range: 500 to 5 mb.
(d) Accuracy: ±5 mb.
(e) Readability: 1.0 mb. or approximately .22 mm on the drum
(f) Weight: 1000 grams
(g) Time accuracy: 10%
(h) Temperature compensation between $ 3 0^{\circ} \mathrm{C} $ and $ - 7 0^{\circ} \mathrm{C} $
Instruments have been built by Lange Laboratories to meet these requirements (the time accuracy figure is questionable).