Here is a thirty minute bar chart of e-mini day session trading over the past two weeks. Tape reading is largely a matter of being sensitive to habits that markets develop and using this information to anticipate the beginnings and the ends of market swings. Volume of trading will either reinforce a conclusion based on a market habit or warn that the habit is changing.
E-mini activity during the rally from the March 6 low is a case in point. On this chart we see three consecutive upthrusts (green rectangles), each measuring 55-60 points. Yesterday's late action put the market at the top of its third rectangle. Volume of trading was the highest in two weeks (red arrows) - right at the top of the rectangle and at the top a 160 point, two week rally.
This was strong reason to believe that a buying climax occurred late yesterday and that the market was about to leave its trending mode and enter a trading range mode. Remember that buying climaxes are usually followed by a reaction and then somewhat higher prices on reduced volume. This is what I am expecting now.
After the market moves above the top of the climax bar at 821 it will be setting itself up for another substantial reaction. My best guess is that such a reaction will carry it down to the midpoint support I have indicated near 781 (purple dotted line).