A "ken" is not a widely recognized unit of measurement in modern systems. However, the term "ken" is more commonly used as a noun or verb in English and has a different meaning.
As a noun, "ken" refers to one's range of sight, perception, or understanding. For example, you might say, "Beyond my ken," to mean something is beyond your understanding or knowledge.
As a verb, "ken" means to understand, perceive, or know. For instance, you might use it in a sentence like, "I cannot ken the complexity of this issue."
In these contexts, "ken" is used to describe one's ability to perceive or comprehend something, rather than a unit of measurement. If you have a specific context in which "ken" is being used as a unit of measurement, please provide more details, and I'll do my best to assist you further.
The term "long reed" does not refer to a standard unit of measurement or a widely recognized term in contemporary systems of measurement. It's possible that "long reed" is used in a specific context or industry, but it does not have a standard definition in general measurements.
If you have more context or specific information about how "long reed" is used, I would be happy to try to provide a more precise explanation.