The MS 261 C-M has all the same great features as the MS 261 – low exhaust emissions, high fuel efficiency and robust performance – but also features the advanced STIHL M-Tronic™ engine management system. With STIHL M-Tronic™, an onboard microprocessor digitally monitors and automatically compensates for changes in your work conditions including elevation, temperature, fuel quality, varying octane levels and dirty air filters.