I think the UV testers are good for a couple of different things. One is to check your bulb over time which will help you determine when to replace it as the output drops off. I've found that several of my Arcadia T5 bulbs lasted much longer than expected in this regard. So keep watching the output from the same distance and replace the bulb if output is decreasing.
The other thing that they are helpful for is adjusting the distance to help create a proper gradient in your enclosure. Ultimately, the adjustments should be done in response to an individual dragon's basking behavior which will reveal their preference over time. The main thing is to offer plenty of options in terms of heat and UVB output and let them choose what they want at a given time. I've found that they tend to bask in spurts but don't spend all of their time in high heat or high UVB areas. Sometimes they just like heat with less UVB, Sometimes they want more UVB with less heat etc. To address that, you can try to set up some areas with high heat/low UVB, low heat/low UVB, high heat/high UVB, and low heat/high UVB. This is where it becomes helpful to have as large an enclosure as possible. There is more discussion about this sort of thing in several old threads
like this one.
To answer your question more directly, The Solarmeter 6.2 is better at monitoring UVB output from a single source - great for detecting deterioration of your bulb over time. I prefer the 6.5 which uses UVI to more closely detect the basking/D3 production range for a reptile and can be used to compare sunlight output to bulbs. I typically suggest 3-6 UVI for basking, but on the 6.2 I'd shoot for more around the 120-180 μW/cm² range across the basking area and a gradient down from there through the rest of the enclosure. At 36 μW/cm² I think your bulb is either too far away from the basking area or needs replacement. How far from the bulb did you take the reading? Was anything intercepting the output from the bulb like a mesh top or other object? Once changes are made I'd just observe for a while. If they avoid the most intense UVB area, reduce the output a bit or try the opposite if they are spending a ton of time there etc.
