(Thanks)

I changed it to this (I realized I didn't need the select() method to do the rc[-3] type thing) and it worked fine:

    $rest = 2*$Meas+4;
    $imc  = 2*$Meas+3;
    $avg->Range(xl_rowcol_to_cell($j-1,2*$Meas+5))->{Value}
      = "=ABS(RC[-$rest]-RC[-$imc])";
..etc..
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