Blood caffeine concentration estimate

caffeine.js

var duration = 24*3600*1000; // 24 hours as milliseconds
var halfLife = 5*3600*1000; // 5 hours as milliseconds
var absorpLife = 3600*1000; // 1 hour as milliseconds
var end = +(new Date());
var start = end - duration;
var numSteps = 24*60;
var step = duration/numSteps;
var startVal = 106;
var rows = [];
var log2 = Math.log(2);
var log95 = Math.log(0.05);
var mymass = 68; // kg
var bloodVolume = 70e-3; // L/kg

function calculateConcentration(events, t, start){
    var sum = 0;
    var e;
    for(var i=0;i<events.length;i++){
        e = events[i];
        if(e.time > (t+start)) continue;
        sum += e.amt * Math.exp(-(t-(e.time-start))*log2/halfLife)
        * (1-Math.exp((t-(e.time-start))*log95/absorpLife));
    }
    return sum/(mymass*bloodVolume);
}

var evts = [
{time: new Date("7/17/2013 1:30 AM"), amt:80},
{time: new Date("7/17/2013 3:00 AM"), amt:80},
{time: new Date("7/16/2013 10:30 PM"), amt:80}
];