Synthetic Trendlines. Vertical distances of A/B and B/C (hi-lo-hi) are used to form a rectangle. The synthetic trendline is then formed by drawing a diagonal line from one corner of rectangle to another. As far as I know, cannot show that process in TV- had to do it with a paint program then draw the lines here. In other words, a rectangle is drawn using those distances as sides of the rectangle, then the diagonal is drawn and that's the Synth Trendline (ST). The ST is then placed at each of the last two points (in this case, B and C). The ST can also be flipped vertical in a paint program.
Comment:
NOTE THAT these lines could've been drawn anytime after the close of the C bar.