Humminbird Helix 7 Chirp Mdi Gps G47" HELIX 7 with MEGA Down Imaging, sharper down imaging detail than standard DI. CHIRP + MDI + GPS, no Side Imaging. Humminbird HELIX 7 CHIRP MDI GPS G4 The Humminbird HELIX 7 CHIRP MDI GPS G4 adds MEGA Down Imaging (MDI) to the HELIX 7 at $649. MDI uses higher frequencies than standard DI for sharper, more detailed views of structure, cover, and fish below the transducer. No Side Imaging at this tier, this is CHIRP + MDI + GPS, optimized for anglers