Currently summariser shows the duration in seconds which is not very readable. 
I always find myself computing the time in hour, minutes seconds.

I propose to change this value to: HH:mm:ss 

replacing:

if (elapsedSec > 100       // No point displaying decimals (less than 1% error)
         || (elapsed - elapsedSec * 1000) < 50 // decimal would be zero
         ) {
            sb.append(longToSb(tmp, elapsedSec, 5));
        } else {
            double elapsedSecf = elapsed / 1000.0d; // fractional seconds
            sb.append(doubleToSb(dfDouble, tmp, elapsedSecf, 5, 1)); // This will round
        }
sb.append("s = ");

by :

sb.append(String.format("%d:%02d:%02d", elapsedSec / 3600, (elapsedSec % 3600) / 60, (elapsedSec % 60)));
sb.append(" = ");