How to make two different graphics appear for positive & negative values

Buongiorno from 2 degrees C snow now melting Wetherby UK :slight_smile:

Before i ask the question please be aware I’m a complete Javascript noob which gives me a temporary license ta ask the ridiculous!

Ok here goes. Ive got a spread sheet that compares one months traffic to another and expresses the results as a percentage illustrated here

Now ive learnt in Google Excel Docs you have to know JavaScript to do what i want. What i want to do exactly is show a green arrow for positive values and a down turned arrow for red using conditional formatiing.

So my question is please:
“What piece of Javascript would i need to look at to trigger different graphics depending on positive & negative values”.

Thanks to anyone that tries to answer this :slight_smile: It aint going to be easy me thinks…