The 45 degree line is an interesting market profile nuance. It occurs when a 45 degree line can be drawn from the lowest point of a distribution to its widest point (TPO POC). This is a sign that sellers have painted themselves into a corner near the lows of the session and creates potential for an upward reversal in the next session. As less and less time is spent the closer you get to the low of the session, sellers are essentially initiating shorts at less and less value. 45 degree line lows should be assumed to be secure until they are breached. The pattern is generally only noted in RTH sessions but they have shown to be relatively reliable signals in overnight sessions as well.
The obvious question is always whether or not the 45 degree line can be drawn in from the high of the day to the POC. Our experience has shown that it is not nearly as powerful of a signal. This is probably due to the fact that short selling is most often a tool of the shorter term trader and longs entering with what seems to be poor location may have longer timeframe outlook.