Here are some of the tips which you can use to calculate faster
http://catdumps.blogspot.com/2009/05/speed-conversions.html
http://catdumps.blogspot.com/2009/05/temparature-conversions.html
http://catdumps.blogspot.com/2009/05/adding-time.html
http://catdumps.blogspot.com/2009/05/converting-kilometres-to-miles.html
http://catdumps.blogspot.com/2009/05/converting-kilos-to-pounds.html
