To put it as an answer I might be able to expand it a little bit.
Measuring ergonomic suitability is really subjective. From my experiences there are obvious guidelines but even those are not clear matrices of numbers. They are more like: Make sure the handle is long enough to support various sizes of hands and is textured to provide grip. Avoid positioning buttons or handles in uncomfortable locations. place the power cord somewhere it doesnt get in the way etc. Do note that ergonomics not only include the ergonomics of using the device, but also about assembling the device. For instance, one should place a screw in a position that is easily reachable and with enough space to place a screwdriver.
However, depending on the classification of the device you are designing, certain "rules" have to be omitted to distribute the product (this also depends on the region you are living in). These rules are mostly about safety guidelines. For instance, in Europe you have the Conformité Européenne (CE) marking. Additionally, there is something like a Declaration of Conformity (again in Europe). This is a set of guidelines a product is expected to follow. For instance: CE dictates that a emergency button has to be colored in an distinctive color (compared to the colors of the device). The Declaration on the other had advices to use the color red with a yellow base (including exact color codes). I certainly hope I explained this correctly because its not that I know these things by heart.
So to come back to ergonomics, the best way to gain insight on how to improve the design is to build a physical model (think of like 3D printing the shape). Test it elaborately in a circumstance you would expect someone to use the device. So if its used in cold weather, expect the user to wear gloves. With a bit of trial and error you can easily define some of your own units to indicate ergonomic suitability.