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Luc is using Mathcad 11 and so he can't read your file. With MC15 you can resave the file in MC11 format, though (something which is not possible with Prime). I attach the file in MC11 format here.

Attaching the worksheet usually is a good idea and quite often simply necessary. But its also a good idea to attach a screenshot, too 😉

Lucs guess was correct. The setting of ORIGIN in your sheet is the default value 0, so every vector starts indexing with number zero. You created a range variable j which started at 1 and assigned values. So vector element with number 1 gets the correct value 4.5 in, but there still exists a vector element with number 0. This is not assigned a value and so its set to zero by default.

To display the vector y.a you typed y.a[j= which only gives you the elements defined by range j, but not the full vector. If you simply type y.a= you see the full vector with the leading zero.

Rule: If you use a range variable to define vector this range should start with the value of ORIGIN.

Here a small example to demonstrate what happened: