| 摘要 |
The slide rule has a fixed support (F) carrying two logarithmic scales (E1, E2) representing illumination (the product of exposure time and luminous intensity) and its inverse. Two cursors (C1, C2) slide along the support, and represent readings from light meters. A sliding rule (M1) carries curves representing darkening of the image for a range of papers or filters, as a function of the illumination. A grey palette across the end of the slide shows the sense of darkening. A third cursor (C3) slides on the rule (M1) to select a grey value.
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