This orange and black paper device has a set of tables printed on both sides of a piece of cardboard that slides between two other pieces of cardboard that are riveted together. The whole thing fits in a cardboard envelope. The tables are used to calculate the total heat gain from light shining through windows and other glass in a building. The instrument was distributed by Libbey Owens Ford Company, a glass firm in Ohio.
A mark on the envelope and the object reads: HEAT GAIN CALCULATOR; A paper sticker attached to the envelope reads: Display Copy Only (/) Please do not remove. A mark on the back of the instrument in the bottom right corner reads: ... 1975, PERRYGRAF Div., Nashua LA. CA 90064 Printed in U.S.A. A mark on the front left corner reads: LOF (/) GLASS (/) 811 MADISON AVENUE (/) TOLEDO, OHIO 43695. A mark on the front of the instrument reads: LIBBEY (/) OWENS (/) FORD (/) COMPANY.
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