Dividing a page equally into halves, quarters etc

Hi everyone,

my question is with regards to dividing a page equally and most importantly accurately in photoshop/illustor/indesign(all CS3) i guess you could think of it as exstablishing a grid.

so to be more specific here are the measurments of my photoshop document:

height: 27.3cm
width: 18.4 cm

so what im trying to do is divde this in to a grid field of 16, ie 4 fields deep and 4 fields high

now what i have tried to do is divide the page in half, so 18.4/2=9.2cm
but the rulers on my page go up in halves so 1,1.5,2,2.5cm so how do i indicate the 9.2 mark accurately. is there a way to make the ruler more accurate?

the same problem goes with the height.

hope u guys can help! ive been wrecking my brains with this one!

also i have some really quickfire questions:

1) should i always work in CMYK and print in CMYK?
2) can someone explain spot color and how to take something to print using it.

thank you and sorry for the overload!

Welcome bogopeas! Photoshop, unlike Illustrator or InDesign, doesn't really have a convenient method for creating a grid. I suppose you could use the slice funtion to do this, but IMHO, it's kind of a pain. I just do the same thing you do, and use math to divide up my image. To get your ruler to read accurately, simply use the zoom function. The larger your image, the more accurate your ruler. I just max out my image size and use the info pallete to place my guides right where I want 'em.

In Illustrator and InDesign, all you have to do is go to the shape tool, choose the grid, and plug your numbers in. Easy peasy.

As for working in CMYK, I never do it. First of all, there are all kinds of commands and options that are only available in RBG. Secondly, let's face it: your monitor is RGB, and the Photoshop images before your eyes are displayed in that format, so it just makes sense to work in that format. But most importantly, I think it's way easier to make color adjustments and whatnot in RBG, and most of the great tutorials you'll find on these subjects will work in RGB mode. I don't convert to CMYK until the very end, as a last step.

As for spot color: There are tons of custom ink colors and ink types that cannot be accurately reproduced through CMYK. In order to get that florescent green or that metal flake gold onto your print job, you'll need another plate on the press besides your four basic colors, which means you'll need another color channel in your Photoshop file. These types of files are usually sent to the printers as PDF files.