Does anyone know if the "free dive" mode in a suunto mosquito should work the same as "gauge mode" in other suunto products like the vytec or D-6? I am wanting to use a mosquito as a back up bottom timer and when I set it in free dive mode it starts out okay but after a while it shows at "Er" on the primary display. I tried two different mosquitos and they both did the same thing so I don't think it is a glitch in the equipment.