Fn + - to set video resolution?

[ctlmd]

My memory is failing me...no not my computer memory...my brain memory...yes, I work on brains, but that's beside the point. I'm trying to install an external monitor and can't remember what function keys to use to control the resolution of the external monitor...I think it's Fn + - and maybe something else to get it to sync with my laptop...it also works with a projector in Red Hat Enterprise Linux. Can anyone please fill in the blanks?
Thanks.

[Icarus]

This varies depending on the laptop model, it's usually BIOS controlled.

Most laptops have it in the function keys with a blue logo of a monitor. My laptop is setup to always echo the laptop display to the CRT output so I don't have to mess around with this.

[ctlmd]

Mine's a Dell Latitude 840. It has a purple Fn key with purple + - and other functions. I think there was something else you had to hold down with the function key while pressing the + or - to set the display properly. If there's another way to do it more permanently, I could try that instead.

[Icarus]

Mines a Dell 600m, got it last year

If the BIOS is simular, you can set it in there to use the dual display (among many other options)