I thought this sounded familiar.  Your Modbus words probably need to be swapped to have the correct value.   Notice I said WORDS, not bytes.  Keep in mind that Buffer data types are 8 bits (bytes), while Modbus returns registers in 16 bit words. This is VERY IMPORTANT - have you been able to actually read a value from your meter?  What is that value?  Do you know what the corresponding floating point value is?    There is no right answer to this.  I know you're trying very hard