Amplifier voltage output error

[esmeco]

I've assembled an amplifier circuit which is composed by a V1 and V2 input and Vo output.V1 is 1V and V2 varies from -5v to +7v with increments of 0.5v.
The formula for Vo is:

Vo=(1+R2/R1)x(R4/(R3+R4)xV2) - (R2/R1)xV1

My questions are:why does the equation |Vo experimental - Vo theory| gives wrong values(Vo experimental is the output I got after testing the assembled circuit and Vo theory is when substituting the values on the equation)?Also,why are the value of the output voltage when I simulate the circuit on microsim different from the voltage theory and experimental output values?Could the experimental value result be influenced by the internal resistance of the measurement device?
Thanks in advance for the reply!

 

[esmeco]

Could anyone help me on this?

 

[berkeman]

What do you get for your calculated, experimental and simulated values? It's kind of hard for us to help you unless we can see a table of the values. And if you could post a schematic of your amplifier, with voltage rails and component values specified that would help. Do you only get errors near the extremes, or do you get errors in the mid-range as well?