Clavis, arithmeticæ: or, A key to artithmetick in numbers and species : Wherein arithmetick and algebra are abridged, demonstrated and made easie, in their several fundamentals and consequents. Collated form the most authentic authors on those subjects, with many improvements and useful theorems, not hitherto extant. Begun by John Parsons, decd. and compleated by Tho. Wastell.