Calibrating computer sound-system clock with GPS

I have added the article "Calibrating computer sound-system clock with GPS." Computer-based watch-timing systems require accurate sound-system clocks. This article shows a cheap and easy way to calibrate the clock.

Focus Stacking

I have a new article on focus stacking.  Focus stacking is needed when the object photographed is smaller than a certain size.  This size does not depend on the camera sensor size or the magnification.  This size (in units of the wavelength of light) is approximately equal to the number of pixels in the sensor.

Winding Demagnetizer Coil

I have added a link to a new article: Winding Demagnetizer Coil.  This describes the construction of a coil for use with my instant demagnetizer.  The secret to good performance is to use a lot of copper, which makes the unit heavy and a bit expensive.