Serfas Bicycle Computers and Heart Rate Monitors
About Serfas - "Wherever your road leads we know cyclists seek the ultimate ride. With that in mind, Serfas is always striving to make products that reflect those wants and needs. Our 20-plus year commitment to quality, performance and customer service is reflected in our innovative products that are rider-tested and rider approved."
Some cycling computers can display a power reading, usually in watts. They usually require a separate sensor - in some cases a special hub or crank arm. A few will estimate the value based on speed, cadence, rider weight or other data. "Optional" means it can read from a separate power meter or sensor. "Included" means it is calculated by the computer or includes the neccessary sensor.