It's also worth noting that there were 2 cubits: a common cubit (18") and a royal cubit (21"). Other nations had their own cubit standards that were not calibrated to the Egyptian standard, and also had the common/royal distinction. So it's important in an article mentioning cubits to specify which cubit was in use.
, Yes, with all of the construction projects the Egyptians were involved in, you think they would be pretty bright about standardizing their weights and measures