Based on your understanding of force balances, guess whether a selected member of the truss is under compression, under tension, or is a zero member. Set the diagonal and vertical point loads with sliders. The reaction forces (blue) are calculated and displayed on the truss. Select "guess force on a member", use the popup menu "select a member" (from 1 to 13), and then select "compression", "tension" or "zero member" from the next popup menu. Check the "check answer" box to see if your guess is correct.