Accutire MS-4021R Digital Tire Pressure Gauge with 8 Valve Caps (2 Pack)

Instructions say gauge is accurate to within 1% + .5psi. So for my tires at 35psi, that would be .35+.5 = +/- 0.85 psi. My "cold" tires were just inflated at the tire store to 35psi. I purchased two identical gauges. On the same "cold" tire the first gauge measured 35.5 and the second gauge measured 34.5. I then calibrated (zeroed) the gauges per instructions by just letting a puff of air hit the gauge, then both read identical PSI for all 4 tires. My four tires measured 35, 35, 35.5, and 35.5. Obviously the setting by the tire dealer's air pump may be off slightly as well, but the fact that the two gauges match, and are either at or within .5 of the tire dealer setting of 35, gives me pretty good confidence that they are accurate.Very easy to use, so now the only question is how they will hold up. Recommend to anyone using in extreme temperatures (hot or cold) to first calibrate (zero) the gauge since its so fast and easy to do.

I bought one of these years ago after seeing a roundup of different gauge where motorcycle enthusiasts tested the accuracy. My mother recently saw me using it and told me to get one for her and my brother. The two pack was obviously perfect for that!I was a bit surprised to find that the new ones are different despite having the same model number. They have added a button near place where you push it onto a valve stem. Apparently, this turns the unit on, where I never had to turn on the one I purchased over two years ago. It was as if the On button was built-in and pushed automatically when checking the pressure.I have come to realize that these have two batteries:-Replaceable coin cells for the backlight and a-“lifetime” lithium battery for the LCD, factory calibration settings, etc.Only the coin cells are user-replaceable. I assume the other is intended to last a “product lifetime” and not an actual human life-span. ;) It’s likely very similar to old Nintendo video game cartridges that sometimes had a lithium battery in them for saving your progress. Many of them from the ‘80s and ‘90s still work despite the expected life being 6-12 years. On the other hand, many don’t work, including games from the new millennium. I’ve had to replace them even in Game Boy Advance games (to be fair: they are smaller), so I t’s a crap-shoot.If you are thinking that you can replace it anyway just like the old video games that aren’t intended to be user replaceable, unfortunately: no. Replacing the internal battery would not restore the factory calibration settings. Without those there would be no reason to use this over any old gauge that might cost less than the replacement battery itself... and that’s assuming it will still work at all. I feel that it should have used an small serial EPROM or EEPROM instead of battery-backed RAM, but I’m no electronics engineer.So, why did I give it 5 stars? Well, all that about the battery was just something I accepted about the old one and I still felt it deserved to be rated very highly. No one else was storing calibration offset values from factory testing of each individual unit to compute a more accurate pressure and that was one way to do it. Next, the revised version with the On button seems to be a way to preserve that internal battery even longer, which is a very Pro-consumer move on their part. They probably kept the same model number because it already has a great reputation. Consumer Reports and others likely reference it directly.If I’m wrong and the button just replaces a hidden button that the original had built in to the pressure port, then it was likely done for cost savings. Again, this is a pro-consumer move, considering that no one else is calibrating them individually from the factory at this price point and it’s probably the only way they could afford to keep doing it. Where the button is, it’s almost impossible to miss. Heck, you’ll probably accidentally press it if you used it exactly like the other one and didn’t even know it was there.If this does anything at all for conserving the lithium battery then it is a very good thing!

I bought two of these and tested them against two other tire pressure gauges I had at home, one an older and much heavier Accutire electronic gauge and an older mechanical pencil type gauge. All four read exactly the same on a 35 PSI tire. As I lowered the pressure in the tire all my gauges tracked my reading within a half pound (which is the resolution of the display). I think the agreement of all four gauges attests to their accuracy. Yes, they could all be wrong, but unlikely. These gauges are very light and I deducted one star as they don't turn on when pressure is applied like my older Accutire gauge. You need to press a little button to get them to light up and measure. Not really a big deal but not as convenient. The only thing that would make these great is if they switched from button cell batteries to AAA to make replacement something that most have in their homes at all times.

Had used one for well over 10 years. Still working well, so I bought 2 more. Stated accuracy is +/- 1% or 0.5 psi, whichever is greater. This is much more accurate than the 3 "stick-type" gauges were. These weren't too bad, but the difference from the MS-4021B was 4, 2 and 1 psi. The difference between the three MS4021B gauges I now own is 0.5 psi. So this much more accurate. Also this model is one of the 2 or 3 recommended by Consumer Reports in their most recent review (albeit a few years ago). Recommended.

For the money this is your best bet for a digital tire gauge. Check the Amazon reviews and check other independent reviews and you will see why. Tire gauge not much good unless you are confident that it is reading accurately. I have tested the 1st one I bought against a high end analog racing gauge and it's within .5 pounds at various pressures. That's pretty good for a $12 gauge. Another thing I like about this gauge is that it has a very positive contact with the valve stem, and is very easy to hold in place with zero leakage. The ergonomic shape really lends itself to ease of use.By the way, remind yourself and others that measurements are generally only accurate if the gauge and tire are at about the same temp, and above freezing. So measure the tire pressure in your garage with cool tires, not right after driving and you'll be in better shape.

Two out of the two I just purchased didn't work straight out of the box. Yes, I followed the directions. I pulled the tab out to make battery contact. I set the display to psi. I tried to measure my tire's pressure...no display. And yes, my tire had pressure...I had checked it first with my old gauge of the same model number. (BTW, I've had 4 of this same model number in the past and had been very pleased with them.) I'm returning these two for replacement...hope they work.