One is the Study Reels which shows one plane in a different attitude and at a different range so that the viewer can learn both recognition and range by examples.
The other set are Test Reels which places 7 different planes on one reel. Each plane is shown at a different attitude and range. The test reels were used as a self-test after studying the study reels.
Each set consists of 75 reels.
Study Reels have all 75 except #51.
Test reels have all 75
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