Potential vs. Current Graph

1. The problem statement, all variables and given/known data

On my potential vs. current graph for resistors in parallel, the slope of the regression line is 8.94 ohm (V/I = R) for a 10 ohm resistor and a 50 ohm resistor. The theoretical value of R_eq is R_eq = 1/[(1/50 ohm) + (1/10 ohm)] = 8.33 ohm. Upon comparing the two R_eq values, I was wondering why the experimental R_eq value is higher than theoretical value. What sources of error could account for this deviation? (Oh, the regression line's y-intercept value is close to 0; it is 0.004 V.)


2. Relevant equations

See above.

3. The attempt at a solution

See above.

Thanks.