Take special care when marking-out a kitchen or bathroom wall for ceramic tiling. This is necessary because floor levels are seldom exactly true, so they should never be relied upon as an accurate starting point.
First, fix a horizontal batten the height of a tile above what appears to be the lowest point on the floor or skirting, making sure that it is positioned accurately by laying a spirit level along its length. Check, by sliding a tile along the floor or skirting, that the tile height is not exceeded at any point along the batten. This is important, because it is preferable to fit the bottom row of tiles by cutting them rather than to leave small gaps that will be awkward if not impossible to fill. If the floor does drop more than the height of a tile, lower the batten so that the biggest gap left does not exceed one tile width.
Next, calculate the number of full tiles needed to cover the full width of the wall and mark where the exact centre of this row of tiles will fall. Fix a vertical batten at this centre point – again checking with a spirit level that its position is exactly true.