Dry Ice Slide Rule

The temperature here is -9°F and still dropping, so I thought it might be an appropriate time to post a picture of this odd little circular slide rule.

Dry Ice Slide Rule

This slide rule belonged to my grandfather, who was a meat inspector for the US Department of Agriculture. The slide rule was used to calculate how much dry ice was needed to fill a railroad car to keep a load of beef frozen until it reached its destination. The back side bears the date 1954.

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