Absolutely!!! you must have a full spool and then it will read right on. When you lose some line it will be off and the more line that is off the worse it will be magnified. I had one that I had lost about 150' off of in the summer when the fish were deep and during a drop, I said put it down to 65' and I watched it on the graph and it was only at 51' as you will see it makes a huge difference.
Here in lies the problem. When you are off that much every time you see fish at a certain depth you will always want to either put it just above them, or in alot of cases you will drop thru them and reel back up above them. So by being off you will never really know where you actually are and it will cost you strikes believe me.
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Eat, Sleep, Hunt and Fish (The Devil is in the details)
Dan Duncan