Just about every camera made in the last 30 years has a light meter...your D40x certainly does.I think I don't have light meter on Nikon D40X
:scratch: You could pound in a nail with a hot dog...but I'd prefer to use a hammer.I want to use manual mode. So I need to estimate the shutter speed
No - there's a meter right in your viewfinder and on the LCD display in the back. In manual mode, set your ISO, set your aperture, and set your shutter speed and the meter will tell you what your exposure will look like. Dead on the zero is what you want. If it's towards the negative side it'll underexpose, and towards the positive side it'll overexpose.I want to use manual mode. So I need to estimate the shutter speed
Well, that's a good starting point...but it may not be what you want. The meter will always try to turn the scene into an image that is 18% grey (mid tone). If your scene isn't 18% grey...then the meter reading will be inaccurate and you will want the 'needle' to be off of the zero. For more into...search Metering.Dead on the zero is what you want.