Plus or Minus Ratio

I am making a factory game where if i put down a factory that produces 1 metal the display will count up 1 metal every 5 second and if i put another metal factory down it will count up 2 metal every 5 seconds. now i put down something that uses metal it will take the amount need away from the metal

what i would like to be able to do is a little display as t weather the metal count is in the plus or minus situation so that i know when to put more metal factorys down

could anyone help me with this please as i cant find anything on it

i am using construct 2 but if its show in construct 3 i should be able to work it out.

Use a single variable to calculate and represent change over time. Adjust this variable by adding and subtracting from it when appropriate. Display the variable.

Thanks for reply

What i want to do is a bit more complex than i explained but i think ive sussed it now any but thanks again