This fell into my hands many years ago from an unknown source, and I made it look pretty and put it up at a permanent link: http://bit.ly/metricmodcalc. This spreadsheet is an excellent resource if you’re interested in experimenting with metric modulation in your music. You can hear the effect in some of my tunes, like Wagering Lights at ~2:03, and Jump Error at ~3:10. You'll have to make a personal copy of the spreadsheet in order to use it.