In reference to the patent: US5829213
How long is this patent in the U.S. and how do you know if it is still valid?
This is a tricky question since the patent laws changed that year
look it up here by patent number:
and learn about how long patents last here:
From the above reference: "All utility and plant patents that were in force on June 8, 1995, or that issued on an application that was filed before June 8, 1995, have a term that is the greater of the “twenty-year term” or seventeen years from the patent grant."
I believe both numbers expire the patent. 5-1-2015 or 11-3-2015
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Always seek a professional opinion on these matters.