| 摘要 |
A protractor 10 comprises a body portion 12 having at least a first straight side, a rotatable element 16 mounted for rotation relative to the body portion 12, a ruler 14 having at least a first straight side, the ruler 14 being mounted to the rotatable element 16, an angular scale 18 indicating the angle between the respective straight sides of the ruler 14 and body portion 12, and positioning means mounted between the body portion 12 and the rotatable element 16 for positioning the ruler 14 and body portion 12 in one of a plurality of pre-determined angular positions relative to one-another, the positioning means includes a plurality of angularly spaced recesses (40, fig 3) and a spring biased latching means (spring plunger 34) for engaging in one of the recesses. |
