No, every base is different and for different reasons.. sometimes its actually just a number in peoples heads like 200.. and nothing gets past 200 on the chart.. or it could be a price where something big happened like news.. and the news produced a bounce and now after that news no one can imagine that coin lower than where that news came out.. so you see, its not mathematical.. but it is easily seen on a chart and then you just set your alerts and wait for a crack..