Always use the ears. The reality is that even and especially with a tuner...your instrument will always be out of tune slightly. Here's a video that explains this phenomenon: Also with fretted instruments...the goal is to play as close to the fret as possible. It is entirely possible to pull a note slightly sharp by playing in the middle of the frets if your pressure is too strong. Playing close to the fret also makes this much physically harder to do if you have uneven pressure between sting gauges. With fretless, there are different kinds of fingerboard substances used that greatly effect the precision required. There is a smaller margin for error on an epoxied board than there is on an oiled board. The value in an epoxied board is an incredible tone with a sitar-like quality added to it. This also depends on the choice of flatwound vs. Rounds. I personally always use rounds on an epoxied board. The growl and character with rounds is beautiful to my ears. I always use lined or marked fretless basses because in a professional setting...I need to know instantly if a problem is occurring with a truss, a tuning key or a neck shift that isn't related to my intonation. The fretmarkers give me the instant information I need while playing that there is a problem not related to accuracy instead of having to test the bass in a controlled environment. The reality is that I'm going to probably have to use that bass for a studio or gig tomorrow or the next day...and I need to know exactly what's wrong in order to get it fixed quickly. Diagnosing on the spot saves a ton of time. I don't care what the purists have to say....it's never once kept me from a gig, a studio or from achieving musical satisfaction. The upright is much easier to achieve pitch because it's scale length offers a larger relative "sweet spot" for the correct pitch. The trade off is the physicality of the Upright hinders certain aspects of playing that can be effortlessly achieved on an electric. Always use the ears first no matter what.