| 摘要 |
A level including an elongate hollow frame with two sidewalls and a topwall extending therebetween. A central vial is within a topnotch formed by removal of a topwall section and adjacent sections of sidewalls including notch-defining bottom and side edges. The frame includes an inner horizontal wall extending between the sidewalls at the notch-defining bottom edges. The central vial is supported in accurate orientation without calibration against a cental-vial reference surface formed in the inner horizontal wall parallel to the top and bottom measuring surfaces and defining a notch-bottom. An integral inner vertical wall extends between the top and bottom walls thereby reinforcing the frame along the frame length. A plumb-vial structure has a viewing-end region and an opposite-end region. The viewing-end region includes an elongate ramp sloping along a level-longitudinal axis toward the plumb vial with an inclination permitting vial viewing from shallow angles. The inventive level further preferably includes an external brace reinforcing a central frame portion weakened by forming the topnotch.
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