If you have a volvo outdrive, it it easy to adjust. Lower drive, loosen 2 bolts and move sensor until someone looking at gage tells you it is where you want it to read.
If the sender is old and going bad, it will quit working. Will not be a sporadic, work one day and not the next.
Hope the sender does not go out on you, they are $140 just for the sender, which I found to be outrageous! Easy fix though.
Here is a photo of sender on a volvo DPS, would look the same on a SX. Center of photo you can see the 2 bolts, loosen them and rotate a tad until you get the gage to read what you want.
As others have mentioned, I dont need to look at the gage to know where the drive is, your going to adjust drive for best performance for given load/speed. You will go by feel.
It is nice to have the gage set for others whom you have pilot the boat, you just tell them to run boat with trim at ?????
Let us know if you need any other info.