In Graphology slant can refer to either upstroke or downstroke values. In Robinson's model, both the downstroke and the upstroke would have been powerful. It sounds similar to clawhammer banjo playing, which emphasises the downstroke. Most thrust is generated on the downstroke of flapping flight. Then the wing is flipped again (pronation) and another downstroke can occur. The downstroke starts up and back and is plunged downward and forward. On downstroke, new mud enters the pipe from beneath and the upper portion is expulsed. A slower downstroke, however, provides thrust. On the downstroke, the water is discharged, through an outlet valve, into the outlet pipe. When the wing moves down, this energy is released and aids in the downstroke.