public static float roundToOneSignificantFigure(double num) {
        final float d = (float) Math.ceil((float) Math.log10(num < 0 ? -num : num));
        final int power = 1 - (int) d;
        final float magnitude = (float) Math.pow(10, power);
        final long shifted = Math.round(num * magnitude);
        return shifted / magnitude;
    }
Rounds the given number to the given number of significant digits. Based on an answer on <a
href="http://stackoverflow.com/questions/202302">Stack Overflow</a>.
hellocharts-library/src/lecho/lib/hellocharts/util/FloatUtils.java