You may notice that the graphs from the data sheet show about half the stretch for VPC at 30% compared with the StaSet graph. It is just that the numbers go up much faster with the StaSet. Basically, the numbers look funny in the graph for the VPC as it is showing really very little stretch slope but has this large offset. They might be confusing construction stretch in there somehow. It looks like the VPC has .7% stretch with no load, which just doesn't make sense.
When I put my calculator together, I just put down the numbers from the data sheets. I really have no basis for doing anything else. I will add a note to that effect.
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