I've been through several tire gauges this year and I think I've finally found one that works.
It's the Slime #20071. They can be found at AutoZone, Wal-Mart, etc. for about half of what the web page says.
On the later model 400s there are dual front rotors, making it a challenge (pain) to check the front tire pressure. With the dual end of this gauge, you can slip it on and check the pressure easier than simply removing the valve stem cover. The rear is just as easy - no need, IMO, for angles valve stems.
There also is an instruction sheet to tell you how to work the memory and other controls (if you want to get that involved). There is also a removable back so that the battery can be replaced - a big plus over other digital gauges that are designed to be throw-a-ways.
I paid about $13 for mine at Autozone yesterday.
I'm going to presume that it is reading on the mark or a bit low since my last Slime gauge product was about 2 pounds low (according to my old gauge), however, I believe it is accurate. It's also small enough, even with the hose wrapped up, to easily fit in the palm of an adult (unless you have really tiny hands and the readout numbers are easy to read.