Clavis usuræ, or, A key to interest, both simple and compound : containing practical rules ... whereby, all the various cases of interest ... may very easily be resolv'd both by the pen and a small table of logarithms, hereunto annex'd ... : to which is added, rules to be observ'd in estimating the value of annuities, or leases, and insurances for lives, &c. : also, the business of rebate or discompt, and the equation of payments ... /