Let's hit the first question off the bat; Do you need this doo-dad to properly build a wheel or keep your wheels in good working order?The answer is it depends upon how close you wish to be to the bleeding edge.Mechanics have been building bike wheels for about 200 hundred years now (dating back to before the early velocipede designs), usually without the benefit of a spoke tension gauge. And for decades, racing wheels used in everything from the Tour de France to serious downhill competitions have been built without spoke tension meters as well. That is because mechanics overbuilt their wheels for the riding style and course, and their fatigue limit was sufficiently far from their elastic limit. (spokes that are tensioned too high are too close to their elastic limit, or that of the rim) Likewise, if you wish to build your own wheels and follow some basic safety factor limits when building a wheel, then a tension gauge is not important. That said, in today's world, there is always that rider out there who is 200 lbs (90.7 kg) and who wants a 24 spoke radially laced front wheel on a 330 gram rim. If bleeding edge riding is your style or you are trying to save 150 grams on your carbon fiber road or mountain bike or you want to push it right to the physical limits, then a spoke tension gauge becomes essential.This Park Tools TM-1 gauge works by using a spoke diameter gauge to measure the middle (or butted part, if your spokes are such) part of a spoke (or you could use precision calipers) and then applying the the tool so that the spoke runs between the two fixed posts and the moveable post. The arrow at the top will point to a number on the graduated scale and you then refer to the separate conversion table to see what kilograms of force (kgf) measurement this corresponds to. For most wheels, you want somewhere between 80 and 130 kgf. Although, this value can vary depending upon the exact riding application. I am not a professional or shop mechanic, but I do build wheels for myself and others that join our off road riding group. I have used this gauge for about twenty wheel builds over the last five years or so. I find it to work fairly well. My older mountain biking wheels (rim brake) are often set up with Mavic 32 hole X517 rims and are typically radially laced in the front and three cross drive/radial lace non-drive in the back. While my newer rims are often 32 hole DT Swiss, Mavic X317 disc or Stans racing rims. I can usually tune by hand and by sound my wheels so that no spoke is 20% above or below the spoke average of the entire wheel (this is a standard reference limit for bike wheels), but the TM-1 really helps me to keep my older wheels at right around 100 kgf and my newer disc rims at about 110 kgf. And these values are right in the happy middle between allowing for a long fatigue life while maintaining ample tension so that if one spoke breaks, the wheel does not taco and I can ride back to the trail head. Those tension levels also prevent fatigue at the rim eyelets and ensure long rim life.Are than any negatives about the TM-1? Not really, but I do find the spoke diameter gauge to be cheaply made. I much prefer to use my Neiko digital caliper when measuring spokes. I also wish that Park Tool would include a standard guide for major manufacturers in their conversion table. The values for a 1.5 mm butted generic spoke from China and one from DT or Sapim are not the same. (Although, you can find these exact values online) And because the gauge is a calibrated spring, I suggest any owner send it back to Park Tool every 25 wheel builds or so, so that exact calibration is maintained. However, those are relatively small quibbles. Thanks to the TM-1, I have never had a wheel taco so far or a spoke break. While this gauge is not essential to wheel building for most riders who are not bleeding edge weight weenies, it does allow the home builder to have some quantitative idea of how their wheels are doing. And for me, that means longer wheel life and no problems on the trail. Five stars in my book.This thing works as advertised. If you are into doing your own bike repairs, this is very handy to take care of your rims and spoke tension. A must to get your wheels right!Does what its suppose to do well. The only thing I would recommend they do is add the measurements on both sides of the tool. Sometimes you have to move the tool to the opposite side of the wheel and instead of trying to read through the wheel, we could just look at it on the opposite side of the tool.I've built a few wheels with and without this gauge. I know that I feel a LOT better knowing that my spokes are not too tight or too loose -and that the relative tension is even all the way around the wheel.There seems to be two schools of thought reading the other reviews. One says that this gauge is not necessary and a good wheelbuilder only needs to tell by "feel" if the wheel has correct and/or even tension. The other is that this is just more information that gives you more exact knowledge of where you are with spoke tension.The question is how does one get this "feel" if one has nothing to compare it to? The old canard about striking the spoke and listening for the correct musical note is a bit funny IMHO. Seriously? There are so many variables with regard to thickness and length of spokes that this seems to me to be just more mumbo-jumbo voodoo.A lot of wheel builders seem to be quite proud of their "mad skillz" and look down on this gauge it seems. Some say "take a wheelbuilding class for $100+ each session and "learn" this feel." I tend to go with the "get the right tool for the job" school of thought. With this gauge you will know exactly where the wheel tension is and it is one less variable that one has to guess about.Many of the reasons why some reviewers put down this tool or say that it is doing "more harm than good" in some circumstances seems to read to me as rationalizations why they or other people shouldn't spend the money on a tool such as this. Most bikes shops I visit have this very tool and wouldn't work on wheels without them. And they KNOW what they are doing. Sure, I think that a person may mislead themselves about how important this tool is with relation to other knowledge about building a wheel but if one is careful and does a lot of reading those other things can be figured out as well. Doing everything else right won't help if you have way too much tension on your wheel and start to damage the rim -or have too little and the spokes fatigue and wear quickly.Perhaps some of the VooDoo practitioners don't like the idea that just about anyone has access to the magic of spoke tension with this simple and inexpensive tool. I can't help but feel that they might be a little jealous/upset that just about anyone from the "outside" can jump ahead miles in their abilities without doing their time under the tutelage of a wheel-witch doctor such as themselves and learning the "black arts" like a proper acolyte.Raleighphile doesn't role that way! Knowledge and skills should be free to learn and all should have access if they only know where to look.One more thing:* the first meter I purchased was defective and was showing a much higher reading than what was actually present. This caused my first wheel build to tensioned WAY too loose. I thought at first that all the wheels I've ever built have been WAY too tight but I checked the gauge against one at the LBS and saw that my gauge was in fact defective. Amazon took it back and gave me another one free of charge with free shipping.It's something to be aware of. I don't know how common this is.I keep the gauge safe in the original box whenever I'm not using it an am very careful not to drop or bang it to get the calibration messed up. Having another gauge around or available to check against periodically might be a good idea. If you are friendly with your LBS I'm sure they will let you use one of their gauges to make sure they are reading the same.I haven't used it yet but be aware that the edges of this thing can and will slice you like a razor. Cut me good just taking it out of the package! It is razor sharp, no joke. A little sandpaper on ALL of the edges and your good to go, knock the edge off the ends of the spring ends too, they're capable of slicing you as well.Love the tool and makes me feel more secure that I'm building wheels properly since I'm just learning the art. The scale is very hard to read for my old eyes. I'm going to rub white paint on it and see it that makes it more visible. Mechanically very well built and although I have nothing to compare it to I assume it is accurate and I place trust in Park Tool.This is a comparative tool and you have to refer to tables to get the absolute measurement. However when checking a wheel you should use the associated app to get a proper appreciation of the readouts. Use in conjunction with a wheel dish guage because although you might have a trued wheel the hub position may be out and when you sit on the bike the anomaly will show up. As an example I got a new front wheel that was trued but the spoke tensions of left and right spokes did not approximate each other and when the wheel was set against the hub, the dish of the wheel was out - a gap of 1/4 inch on the rim on the left side.I don't mind using returns or 2nd hand tools, BUT not when I have paid full price for a brand new tool. The tool is marked where it has been dropped, and it has light scratches on it. The scale for reading tension is barely legible.The instructions saythe meter is calibrated at the Park Tool manufacturing facility. Ha ha ha.The tool is not even zeroed.Positives: Works well, easy to understand and work with - I set 28 spokes to around the same tension in about 15 mins although not able to get a clear target value from the spoke manufacturer to aim for. Easy to resell.Negatives 16" wheels - will only work on radial patterns, cannot use on the interlaced rear wheel of my Brompton as insufficient clear length to fit the meter. The tension posts are 106mm apart and really need 116mm of clear spoke to comfortably get a reading Expensive for the amount of use I will get from it.The park tool tension meter is adequate for the amateur, it is not consistently accurate and therefore it is important to take several readings per spoke. That said I have used it quite a lot now and each time i get better at using it and consequently my wheels are pretty bang on now. I would like to try it side by side with a professional meter but haven't as yet committed to the extra cost (around £200 as an average) but I may well do one day soon.If you are the patient type and you really need to be with bicycle mechanics then this tool will do what is required and you should be satisfied.It works easily enough but is massively overpriced. You probably don't need a tension meter; all the wheels I've built in the last 20 years turned out to have good tension of 120 to 150kgf. However, some modern rims have a lowish maximum tension recommended by the manufacturer and it saves you guessing.