| 摘要 |
<p>The figure shows an educational apparatus (10) or toy plane table for teaching the principles of surveying, practical geometry and map making. The apparatus (10) comprises a table (21) mounted on a tripod having telescopic, height adjustable legs (11). The table (21), which is rectangular, has an aperture (22) at each corner, and held captive in each aperture (22) is an associated paper retainer. Each retainer (24) wholly lies flush with the table (21) but has spring mounting means (26) enabling it to be selectively raised to receive a corner of a sheet of paper and to spring back to its usual position to hold the corner of the sheet tightly against the table (21). The apparatus (10) may be provided additionally with a plumb bob (30). The table (21) may also have an alidade (31) mounted thereon.</p> |
