Proportional error for Atwood's machine lab

[atir.besho]

I have attached the lab

right now I am stuck on proportional error in multiple variables

I want to take the lab step by step so i can learn how to do calculate all the variables from now on.

I have lab partners during the lab but I am completely clueless when I am working on it on my own.

Can someone just explain the formula needed to get the proportional error please?
I know I need 1 gram as uncertainty.

 

[Simon Bridge]

For independent measurements $x\pm\sigma_x$ and $y\pm\sigma_y$, the proportional errors are given by:$$p_x=\frac{\sigma_x}{x}, p_y=\frac{\sigma_y}{y}\\
z=xy\implies p^2_z=p_x^2+p_y^2$$