Mathematica treats the exact integer number 1 differently from the approximate floating point number 1. Approximate numbers are indicated by including a decimal point. So
"Va ->.0005 (-10000. - 1. deltaR)"
means to substitute for all Va the approximate .0005 times the expression (approximate 1000. - approximate 1.0 times deltaR)
For many simple tasks there is little difference between using approximate and exact numbers, but for some problems this makes considerable difference.