iBike Dash with Power Cycling Computer with Power Meter for iPhone 3G/3GS/4 and iPod Touch Includes a combined speed/cadence sensor and heart rate strap for enhanced fitness feedback and interval training. Large, full-color, easy-to-read backlit screen Memory size: uses iPhone/iPod Touch internal memory for essentially unlimited ride file lengths and numbers of ride files Windows System Requirements: Windows XP/Vista/Windows 7, Macintosh System Requirements: Intel Mac running OSX 10.5+ Easy mid-ride spare battery changes extend ride time length, without losing data or interrupting ride (extra spare batteries not included)