SUB Euler_Richardson(x,y,vx,vy,t,C,g,dt,dt_2)
    LET v2 = vx*vx + vy*vy
    LET v = sqr(v2)
    LET ax = -C*v*vx
    LET ay = -g - C*v*vy
    LET vxmid = vx + ax*dt_2       ! velocity at midpoint
    LET vymid = vy + ay*dt_2
    LET xmid = x + vx*dt_2         ! position at midpoint
    LET ymid = y + vy*dt_2
    LET vmid2 = vxmid*vxmid + vymid*vymid
    LET vmid = sqr(vmid2)
    LET axmid = -C*vmid*vxmid     ! acceleration at midpoint
    LET aymid = -g - C*vmid*vymid
    LET vx = vx + axmid*dt
    LET vy = vy + aymid*dt
    LET x = x + vxmid*dt
    LET y = y + vymid*dt
    LET t = t + dt
END SUB