Crystal model 1920
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An Crystal model with three colored thread axis, white – yellow – red. A mathematical pane has the property that the axis are 90 degrees to one other, the axis, red, yellow and blue line, are in 90 degrees to one other. The old glass have a small  crack of 1,6 cm by the red thread axe, . The tape have a test of time. Further in good condition. Measurements 11,5 x 9 x 14,5 cm.
