Shuttering the arsenic flux off and on is known to induce reflection high-energy electron diffraction (RHEED) intensity oscillations during continuous molecular beam epitaxy growth long after the regular oscillations have damped out. These RHEED intensity oscillations are shown to be useful for quantifying the flux variations from group III cells. Flux transients froin opening the gallium and aluminum shutters, and intentional flux changes produced by changing cell temperatures have been accurately measured using this technique. After opening a group III shutter, two transients have been observed in this system. In the case of gallium, a relatively short-time transient less than 300 s long is typically observed. This short time transient is characterized by a 3% drop in the flux. Sometimes, however, a longer transient with a time constant of about 20 min occurs. The longer transient usually gives a 3% to 4% rise in the growth rate. The aluminum cell consistently displays only a long-time constant transient. Intentional rates of change in growth rates are also easily measured with the induced RHEED intensity oscillations. For example, near a 1 mum/h growth rate, linearly increasing the gallium cell temperature by 15-degrees-C over 5 min results in a linear rate of change in the growth rate of 11.0+/-0.5 (angstrom/h)/s. Linearly ramping down the gallium cell temperature by 15-degrees-C in 5 min results in a rate of change of -12.4+/-0.7 (angstrom/h)/s.