Google Apps Triggers

Google Apps triggers enable code to be executed in response to events such as editing the spreadsheet or on a timer. You set up a trigger in a spreadsheet as follows:

Log into Google spreadsheets using the user: hdx.gapps.triggers@gmail.com from /wiki/spaces/HDX/pages/38551804.
Go to the menu Tools -> Script Editor in the spreadsheet. This opens a new script editing window.
Enter the code for your trigger into the Code.gs tab as a function.
Then go to the Resources menu and select Current Project's Triggers.
Click on the link which says "No triggers set up. Click here to add one now." and set up your trigger as desired using the dropdown menus, putting your trigger's function name under "Run".
Click notifications and from the Execution failure notifications dropdowns, choose the hdx.gapps.triggers@gmail.com email you want to use and set when to notify as "immediately".
A prompt may appear asking you to grant permissions to the user hdx.gapps.triggers@gmail.com which you should.

The reason to use hdx.gapps.triggers@gmail.com is that it is not possible to see another person's triggers so multiple people could mistakenly create the same trigger on a spreadsheet.

Note that the hdx.gapps.triggers@gmail.com user only needs read access to the spreadsheet for the purposes of the trigger. Write access is only needed for adding the code for the trigger to the Script Editor (which can be completed with a different user). If the hdx.gapps.triggers@gmail.com user only has read access, you will not be able to open the Script Editor from the spreadsheet, you will need the direct url (which you can get by opening from the spreadsheet with another user that does have write access).