Knowledge of how to give cattle injections or shots, be it sub-subcutaneously (SQ; under the skin), intramuscularly (IM; directly into the blood supply of the muscle), or intravenously (IV; directly into the vein, usually the jugular vein), is very important in order to be able to vaccinate or treat cattle with vaccines or medicines, respectively. A cow, bull, heifer, steer or calf does not have to be sick in order to be given an injection, many cattle that are perfect healthy are required to get injections or shots for annual vaccinations or booster shots.
The main loop (the area of the embedded code where the fuel pulse width is calculated) for MegaSquirt-I normally runs at about 1500 Hertz (1500 times per second) and can wander a couple hundred Hertz either way depending on whether you are in cranking mode or whatever else is going on and needs attention (these are called interrupts). For MegaSquirt-II, the main loop runs about twice as fast. For example, in a pretty reasonable worst case, 1500 Hz is about 4 times the IRQ (" interrupt request ") rate (6000 RPM * 8 cyl = 400 Hz). So on a V8 at 6000 rpm, the fuel pulse width is updated 4 times between each spark event (and 8 times between fuel injection events, if running 2 squirts). MegaSquirt-II doubles these, as would running a 4 cylinder (since there are half as many events at a given rpm). At 600 rpm, you have 10 times as many updates per ignition/injection event. To further understand the equations, read the VE Tuner document . This document describes one implementation of the autotune that was not finished at the time that document was written. The top section has the equations for the MegaSquirt ® fuelling.