When I started fmq, I tried to keep a record, but since then, I adjust tension every time I turn my machine on. The different types of fibers that make up threads are susceptible to changes in heat and humidity. These slight changes can effect your thread. My Baby Lock Tiara doesn’t have a numbered tension knob. I do have a Towa gauge, but only use it if I am using a new to me thread in my bobbin. I quilt with cotton, polyester, metallic threads, and clear nylon threads. I just keep small quilt sandwiches around for setting my tension. And always check your threadpath, if you miss on spot it really throws everything off!