Hi Bob, Is it 0.71 ppb off or 0.071 ppb off? This is how I calculated it: 139390000010/13939 = 10000000.000717411579022885429371 answer/10000000 = 1.0000000000717411579022885429371 answer-1 = 7.1741157902288542937083004519693e-11 answer*1e9 = 0.071741157902288542937083004519693 Thanks, Alan