Need help create momentary switch code..xml

Hello,I'm trying to program a fuel test button using xml. The switch in the real aircraft (DC-9) is momentary ...test is active only while the mouse button is held down.The test works such that when the test button is held the fuel gauge needles will slowly move torwards empty. When the test button is released the gauge needles will move back to tank quantity values.I'm thinking of coding this like....Create a global variable with the test button gauge = L:FUEL_QTY_TEST = 1 or 0The fuel gauges will contain a case statement for the L:FUEL_QTY_TEST variable case 0 (test active) needles get value of tank empty case 1 (no test) needles get value from FS FUEL...QUANTITY variablesIn concept it seem that it should work... I'm just running into problems actually coding it.Can someone assist me?Thanks,John