Ok, if you take say a Bollinger Band (maybe read Kathy Lien) I used to use a Double Bollinger Band with the deviation set at 100 and 200 percent. Picture a standard deviation bell curve. The simple version is use the center line as the start of the center between S&R, the mean deviation. A trade can only move so far in a bull or bear bias, this is measured as deviation from the mean. Of which all indicators are based.
Trades will roughly coincide with the 1% and 2% or greater with the percentage. This will enable to trader to place odd on when to enter a trade. In my Bollinger Band example anything in the 100 or 1% rage is a channel, out side 200 or 2% is overbought or oversold.
Most folks trade from the mean outward, I would do exactly the opposite, once the PA passes the 2% wait for a commiteds reversal and then trade back to the mean and beyond to the opposite 2% signal. Its all Moving averages.
Now if you combine that with an oscillation say the CCI (my fav) or the Stoch you have a very forcaster of momentum and trade confirmation.
There you have a trade strategy and an over simplification of percentage of deviation.
Now if your math knowledgeable and I am not what your really want to know is variances. That’s why I have moved to strength and weakness identification because that the momentum of why a currency pair moves.