Best ticks for Y axis

bestTick.js

function bestTick(largest, mostticks) {
    var minimum = largest / mostticks;
    var magnitude = Math.pow(10, Math.floor(Math.log(minimum) / Math.log(10)));
    var residual = minimum / magnitude;
    var tick;
    if (residual > 5) {
        tick = 10 * magnitude;
    } else if (residual > 2) {
        tick = 5 * magnitude;
    } else if (residual > 1) {
        tick = 2 * magnitude;
    } else {
        tick = magnitude;
    }
    return tick;
}