With this latter (H/L) method, you ignore the level at the close and simply ask yourself, 'during the day, did the price achieve a higher/lower level and in doing so fill a box to the upside (or downside)?' If yes, you mark a new X or O, depending on the direction of the price.
These H/L charts can often throw up quite different pictures compared to those based on the closing price/level. Take the FTSE 100 for example:
This is a 'noisy 10x3' high low chart, ie each box represents just 10 points on the index and to reverse each column requires a (10x3) 30 point movement in the opposite direction. This chart is currently showing an intense battle going on between the bulls and the bears, with 6,090 marking the line in the sand. At this level, the bulls have been batted back on three occasions since the turn of the year. There is clear resistance at this level. As a general guide, the greater the resisistance, the more powerful the move to the upside once the resistance is broken (the same applies for breaks of support in down markets) so this 6,090 level is one the bulls will need to take out for the rally to continue.