of the slider 50 the cable 48 is connected to the slider 50 and runs toward the rear end plate 26 around the fixed pulley 44 into the sliding tube 52 back toward the front end plate 24 around the moving pulley 46 and back to the rear end plate 26 where it is permanently attached the moving pulley 46 is attached to the main spring 42 on a first end 41 of the main spring 42 the main spring 42 is attached to the front end plate 24 at a second end 43 of the main spring 42 both the main spring 42 and the moving pulley 46 are entirely constrained within the sliding tube 52 the sliding tube 52 is connected at a first end 55 to the front end plate 24 and at a second end 57 to the rear end plate 26 the sliding tube 52 has an aperture 76 in which the fixed pulley 44 is located and through which the cable 48 passes the slider 50 slides along the sliding tube 52 in operation the umbrella unit 10 is opened by pulling the control strip 68 which effects movement of the slider 50 within the channel portion 74 in the direction of the front end plate 24 in this way the moving pulley 46 is caused to move in a direction opposite to that of the slider 50 or equivalently towards the rear end plate 26 movement of the moving pulley 46 toward the rear end plate 26 brings about extension of the main spring 42 in this way the slider 50 tends increasingly to resist further movement.