I would also like to mention that the new Helix 9 models are bigger screen sizes than the old 900 series Humminbirds.

Humminbird 999 = 8" screen The 999ci HD SI Combo features a super bright LED backlit 8" display.
https://www.humminbird.com/productDetail-Lifestyle.aspx?id=1667

Helix 9 = 9" screen The HELIX 9 SI GPS features a super bright LED backlit 9" display.
https://www.humminbird.com/productDetail-Lifestyle.aspx?id=7674