The upper line is the 2/3 speedline and the lower is the 1/3 speedline (dividing the vertical line in 2/3 and 1/3 respectively )
When an uptrend is in the process of correcting itself, the downside correction will usually stop at the higher speedline (the 2/3 speedline). If not, prices will drop to the lower speedline (the 1/3 speedline). If the lower line is also broken, prices will probably continue all the way to the beginning of the prior trend. In a downtrend, the breaking of the lower line indicates a probable rally to the higher line. If that is broken, a rally to the top of the prior trend would be indicated.