| 摘要 |
<p>A spirit level has one or more vials with light bulbs located adjacent to them. The light bulbs are powered from a battery which is incorporated in th body of the spirit level. Operation is by means of a slide or push-button switch mounted next to the battery. Illumination of the vials in this way permits the bubbles and the datum marks to be seen under poor ambient lighting conditions, thus permitting quick exact measurements to be made even in the dark.</p> |
