Did I have both units at the same time? Well for the first hour or so I only had the 899 on at the console because I was just idling around with my trolling motor out of the water. When I was at the front with the trolling motor down, both units where on, 859 switching between 2D and DI mode, and the 899 I was switching between 2D, SI and DI, so I could see what returns I could or could not see in each mode.