Thanks for the info. As far as the light meter goes, I plan on taking a simple but decent lux meter and wiring it into a TI-84 in order to achieve a more accurate exposure using the equation above. Would that equation work for the programmed "back-end" of the meter software? The "z" value would be determined using the same curve (voltage vs. lux) the manufacturer used, but on the calculator, thus giving the TI-84 the same exact reading as the lux meter would have come up with itself, but without the need to punch it into the calculator manually. Then, using the equation I have outlined above, an f/stop value can be automatically determined by the calculator. This would allow me to use a cheaper lux meter, and would give me greater control over the variables at my disposal. If I am not mistaken, there are four variables available to a film-maker when calculating exposure: lighting, stock (specifically stock speed), exposure time, and the f/stop of the lens. Since the f/stop is the easiest to modify, it would make the most sense to use the other three variables to determine the best possible value for the f/stop. Since film speed and exposure time would remain constant, I could use the calculator to create a simple relationship between the f/stop and the light falling on the scene. I have the physical and electrical aspects of this DIY light-meter project under control, its the equation for a nice "medium-tone" exposure that I am most worried about. How many decimal places should I carry the f/stop number out to? How much of a change in the f/stop value will cause noticeable changes in the final product?