M_DOOM Graphic Alignment

[Scotty]

I am trying to implement an M_DOOM graphic into a wad, but it does not align centrally, instead being offset to the right and clipping off the side of the screen. The graphic also seems to be somewhat big onscreen. I have examined other wads and have used a similar sized image, so i cannot understand what is happening here. What controls how the M_DOOM graphic displays in-game?

[Linguica]

In general you align graphics onscreen by tweaking the offsets, which are listed at the bottom of the window in SLADE.

[Scotty]

Bang on, thank you.