function relative(ms) {
    var sec = 1000
        , min = 60 * sec
        , hour = 60 * min;

    function n(n, name) {
        n = Math.round(n);
        return n + ' ' + name + (n > 1 ? 's' : '');
    }

    if (isNaN(ms)) return '';
    if (ms < sec) return 'less than one second';
    if (ms < min) return n(ms / sec, 'second');
    if (ms < hour) return n(ms / min, 'minute');
    return n(ms / hour, 'hour');
    // TODO: larger than an hour or so, we should
    // have some nice date formatting
}
Format `ms` in words.

@param {Number} ms
@return {String}