FileMaker Pro Custom Functions

/* Returns the Gaussian (Normal) probability integral to the left of x--the left-tail probability. For right-tail probabilities, call with argument -x. Algorithm is #209 from the ACM, by D. Ibbetson. Also used in TrueBasic Stat1 Library. Should be accurate to 8 decimal places. */ Let ( [ ya = (Abs(x)) /2 ; w = ya^2 ; za = (( .000124818987)*w - .001075204047)*w ; zb = ((za + .005198775019)*w - .019198292004)*w ; zc = ((zb + .059054035642)*w - .151968751364)*w ; zd = ((zc + .319152932694)*w - .5319230073)*w ; ze = (zd + .797884560593)*ya*2 ; yb = ya-2 ; zf = -.000045255659*yb ; zg = ((zf + .00015252929)*yb - .000019538132)*yb ; zh = ((zg - .000676904986)*yb + .001390604284)*yb ; zi = ((zh - .00079462082)*yb - .002034254874)*yb ; zj = ((zi + .006549791214)*yb - .010557625006)*yb ; zk = ((zj + .01163044731)*yb - .009279453341)*yb ; zl = ((zk + .005353579108)*yb - .002141268741)*yb ; zm = ((zl + .000535310849)*yb + .999936657524) ] ; Case ( x = 0 ; .5 ; /* special case for origin */ ya ≥ 3 and x > 0 ; 1 ; ya ≥ 3 and x < 0 ; 0 ; /* way out in the tails */ ya < 1 and x > 0 ; (1 + ze) / 2 ; ya < 1 and x < 0 ; (1 - ze ) / 2 ; x > 0 ; (1 + zm) / 2 ; x < 0 ; (1 - zm) / 2 ; " " ) )
 Then copy & paste into FileMaker Advanced's Edit Custom Function window.