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.