The mariners magazine, or, Sturmy's mathematical and practical arts containing the description and use of the scale of scales, it being a mathematical ruler, that resolves most mathematical conclusions, and likewise the making and use of the crostaff, quadrant, and the quadrat, nocturnals, and other most useful instruments for all artists and navigators : the art of navigation, resolved geometrically, instrumentally, and by calculation, and by that late excellent invention of logarithms, in the three principal kinds of sailing : with new tables of the longitude and latitude of the most eminent places ... : together with a discourse of the practick part of navigation ..., a new way of surveying land ..., the art of gauging all sorts of vessels ..., the art of dialling by a gnomical scale ... : whereunto is annexed, an abridgment of the penalties and forfeitures, by acts of parliaments appointed, relating to the customs and navigation : also a compendium of fortification, both geometrically and instrumentally / by Capt. Samuel Sturmy.

As for Example.

Admit the Magnetical Azimuth by the Needle, is	59 deg. 33′
And the Suns Azimuth found, as before, is	48 - 18
The Variation is — the difference West	11 deg. 15

So the Magnetical Azimuth being more than the true Azimuth by 11 deg. 15 min. which is one Point of the Compass; therefore it shews the Variation to be one Point, or 11 deg. 15 min. Westerly.

And suppose the Course by the Compass be East 8 Points from the North or South, or 90 degrees; and let the Variation be 11 deg. 15 min. to the Westward.

I demand the true Rumb;

Mr. Borough observed in 1580 d. 11 deg. 15 min. Variation Easterly in Line, House, Fields.	The Magnetical Rumb	90 d. 00 m.
Substract the Variation Westerly	11 d. 15
there remains the true Rumb NE	78 d. 45

Mr. Gunter 1662 found 6 deg. 15′

So that if the Variation be Westerly, you may concieve by looking upon the North-Point; by the Variation one Point, that it being Westerly, it is always accounted to the left hand, so the North-Point, is one Point to the right hand of his true place; and you must Sail N by W, to make good a North way, and W by S to be a good West, and S by E to be a direct South, and E by N to make good an East Course, which will make an Angle with the Meridian of 78 deg. 45 min.