A Gann arc is usually produced by starting with a key low or high and placing the first arc at the nearest key high or low respectively. But in the case of an asset like Bitcoin where extreme growth is still very much on the table, an interesting study is produced by drawing the first arc of Gann's Square from Bitstamp's all-time lows of $2.22 to 2013's rally top....
I have rather consistently found that when price rallies past an arc without correcting or consolidating inside it or immediately outside it for a length of time, price will continue to rally to the next arc, form a top there, then proceed to dump back down to test, at the very least, the top of the skipped arc. Here, look for a top inside or immediately outside...