Hi- I just got a Treasure hunter all vision pro with a 10" spider super coil. It says it has a depth readout, which I assumed would tell me how deep objects were, but my instructions say nothing of that nature. So what exactly is a depth readout, and how do I use it? =) Also, does anyone know if I can use this in shallow rivers, or in the shallow ocean with just the coil in the water? Thanks so much! I am so excited to use my new metal detector=) - Megan