Short rows, I'm not sure if they are a blessing or a curse but I do a lot of them. If you are unsure about what you're doing or just want the added confidence, definitely if you've worked a lot of your pattern before the short rows, use a lifeline before you start the short rows. If you have need to frog the short rows the lifeline will be your absolutely best friend at that moment. Ask me how I know.
I should never overestimate my basic arithmetic skills.