An astronomer needs a telescope and someone that collects and studies German World war 2 helmets needs a USB Microscope.
Let’s get acquainted :
The USB microscope is a digital magnification device. You plug it in your computer’s USB port and you can zoom in and view everything on your computer screen. You can take pictures and make comparisons.
I use 2 models : The first one is a tabletop model which is now 7 years old , it’s a 2 megapixel device which can zoom in 25x or 200x.
Below you see my example pointed at a decal and how the close-up looks on screen.

My other model is a portable one ! I acquired that one in 2015. It’s great for taking with you on fairs and it has come in handy a couple of times. It can also be used as a tabletop like the example above but the quality difference between the two is huge so at home I always use the tabletop one.
Below you can see how the portable version works. Showing the close-up on the small LCD screen.

Price wise you are looking at 150 – 200 euros/dollars. (for either model) Cheaper models exist but I cannot guarantee the quality is sufficient.
It’s a tool not a magic 8 ball
I will counter my own title here but in some case it can by a magic 8 ball and tell you exactly that what you are looking at is fake.
But in order to master the USB microscope decal knowledge is required , before you invest in an extra set of eyes get to know the decal designs and on what shells they should be on.
As it now stands the majority of fakes 99% can still be detected with the naked eye by an experienced collector. If you are less experienced the USB microscope will offer you that extra that you may need to make a call.
Which one should I buy ?
There will have been a lot of changes to the specs since 7 years ago. Important is that more zoom is not necessarily better. Personally I would go for max 200x.
2 megapixels is sufficient but more should be better in this case. The software included can also limit you. If at all possible see if what image preview sizes you can have 1280×960 is good , higher is better. Lower is to be avoided.
The future
Knowing how period decals should look at 200 zoom is firm road block we can throw in front of anyone that is in the business of producing fake decals , to be honest I even think we blocked them completely and forever. Remember a faker does not just need the decal , he needs a shell to match. Preferably wartime painted and with wartime liner , there’s just a finite number of those around which makes it a whole less interesting to put effort into it.
German Helmet Vault
I will keep adding USB microscope close-ups to the decals pages of this website , if you have a microscope you can easily compare them.
Here’s an example that shows the power of this tool. Let’s look at the decals of this camouflage helmet.
The swastika of the Eagle at 25x zoom
The wing of the eagle at 200x – It’s important to have comparables so you know what you need to see.
The tricolor at 25x zoom , you can see the red of the tricolor through the paint cracks.
The black part of the tricolor at 200x zoom. In this damaged area you can see the black on the edge of where it was damaged , the white residue would be the backing paper / glue the decal was printed on.