What I don't understand is why don't they hire somebody to read the text and straighten it out.
Actually, there is a reason why this isn't done. With technical product documentation, you have to have a working knowledge of the language, the technology, and the product. Take, for example, the line I quoted from the DMM manual:
hFE hole: to measure hFE of triode
There's nothing wrong from a language perspective with triode, but it's horribly wrong from a technology perspective. How many people outside of the engineering field would know that hFE is a transistor parameter?
I have to correct the work of tech writers all the time. Their English is great, but they often change the meaning of the original material because they don't understand software terminology.