If I want to find the resistance(R) from a voltage(V) vs current(I) graph for a given wire using the relation tan Θ (slope) = ΔV/ΔI = R, do the scales on the axes need to be the same, independent of the units? Such as, "2mm on the x-axis=0.01A and 2mm on the y-axis=0.01V" or "2mm on the x-axis=0.01mA and 2mm on the y-axis=0.01V"? Or can the scales be different? Does this apply for all graphs where we use the slope or area of the graph to calculate things?

If I want to find the resistance(R) from a voltage(V) vs current(I) graph for a given wire using the relation tan Θ = ΔV/ΔI = R, do the scales on the axes need to be the same, independent of the units? Such as, "2mm on the x-axis=0.01A and 2mm on the y-axis=0.01V" or "2mm on the x-axis=0.01mA and 2mm on the y-axis=0.01V"? Or can the scales be different? Does this apply for all graphs where we use the slope or area of the graph to calculate things?