Flipping a coin - Relative Frequency

A football referee always used a special coin to toss for ends. She noticed that out of the last twenty matches the coin had come down heads far more often than tails. She wanted to know if the coin was fair, that is, if it was as likely to come down heads as tails. Can you help her decide if it is fair or not by clicking on 'flip' lots of times? If you increase the number of trials, is it a better or worse estimation of the probability?