Without a flash, and in manual mode, if I change the aperture or shutter speed I can see the exposure indicator change from positive (+) or negative (-), then to zero. And I can be reasonably confident that my photo will be properly exposed if the bars are at zero (or near).
However, whenever I turn on the flash it doesn't seem to have an effect on the exposure indicator reading. I might see five bars on the negative side of the exposure indicator, so that will prompt me to open the lens until the meter reading is close to zero. The problem with this is that I don't know if the flash will actually cause an overexposure.
Does anyone have any basic tips on how to adjust the aperture and shutter speed when a flash is being used in manual mode? How do I know if my adjustments or too much or too little?