One of the struggles we have had with NFC devices is their varying degree of strength in readers and devices.  
Now we can put a quantitative number to how bad they are.  These field meters are tuned to detect any standing NFC field.  
They will display a value of 1/10vm or 1mH (megaHammy). 
They "used to" come in 4 different colors (Red, Orange, Blue, Green) that will be selected at random. (if you put in your order notes prefference i will do my best to accomodate).I cannot guarantee accuracy.  But i can guarantee that the meters are accurate to themselves.  Meaning each meter will display the same value across each other. If in the future i can get my hands on more precise NFC field testing equipment i can zero these in more and will update with future version releases.
*Note* 
These require a CR2032 that will not be included due to shipping regulations.Also do you love the Idea of this but want to read those Pesky duty cycles.  Perhaps look at the Field Meter Pro
Also note:  due to the recent sky rocket of the led module.  Red is the only color option available for the future.  Sorry all