I have a function: $$ LogC= (LogA - 0.80 * LogB - 8.40)/0.50 $$
Here LogA and LogB have errors. So I know that if $$LogC=f$$then the error of f is $$df=\frac{\partial f}{\partial a}da+\frac{\partial f}{\partial b}db$$ and so on. Here i cannot be sure that a should be A or LogA and b should be B or LogB. Where da and db is the error of a and b.
So I'm asking that which one is correct way to calculate error of LogC:
$$dLogC=\frac{\partial LogC}{\partial LogA}dLogA+\frac{\partial LogC}{\partial LogB}dLogB$$ or $$dLogC=\frac{\partial LogC}{\partial A}dA+\frac{\partial LogC}{\partial B}dB$$