The actual print procedure involves a wide range of parameter controls. The ink is deposited onto the shirt by pulling a squeegee across the surface of the screen. The squeegee forces the ink to come in contact with the garment where it sticks after the screen is lifted. The downward pressure that is exerted on the squeegee blade is a major determining factor in the amount of ink deposited. Lower screen meshes will also allow more ink to flow through them. After this print stroke a second bar travels across the screen in the other direction. This step is called 'flooding' and reloads the screen with ink for the next print. The amount of pressure exerted in flooding also plays a part in the amount of ink deposited. The angle of the squeegee blade also has a great effect on the print. Other critical factors are the speed of print and flood strokes, the thickness and opacity of the ink and the distance between the screen and the shirt. All of these factors must be carefully orchestrated to achieve acceptable results, especially in cases of half tone reproduction. If the print is on dark garment a flash is often required. The flash heats the ink so that the following colors will have and opaque base to sit on. Flashing requires attention to heat and timing and must be adjusted as the platens warm up and the ink changes consistency. Most of the critical adjustments required to control the process have to be done intuitively. Very few presses have any kind of quantified gauges for reading angle pressure or speed in any kind of absolute terms. It is because of this that screen printing is a specialized craft that requires a wealth of experience.