The description and use of a joynt-rule fitted with lines for the finding the hour of the day and azimuth of the sun, to any particular latitude, or, to apply the same generally to any latitude : together with all the uses of Gunters quadrant applyed thereunto ... / contriv'd & written by J. Brown, philomath.

1. To Rectifie or set the Rule to his true Angle.

OPen the Rule to 60 degrees, which is done thus, (indifferent∣ly:) make the lines on the head, and the lines on the other leg, meet in a streight line; then is the Scale of Al∣titudes and the line of Hours set to an Angle of 60 degrees, the rectifying point, being the center of that Angle; Or to do it more exactly, do thus: put one point of a pair of Compasses into the rectifying point, then open the other to 10, 20, 30, or 40, on the Scale of Altitudes, the Compasses so opened, and the point yet remaining in the re∣ctifying point, turn the other to that margenal line in the line of hours, that cuts the rectifying point, and there stay it; then remove the point that was fix∣ed

in the rectifying point, and open or shut the Rule, till the point of the Compasses will touch 10, 20, 30, or 40, being the point you set the Com∣passes too in the Scale of Altitudes, in the innermost line that cuts the center, and the rectifying point, then is it set exactly to 60 degrees, and fitted for observation.