A device for marking a surface, the device comprising: a body configured to store a marking substance; a guide arrangement having a first end and a second end, at least a portion of an outer surface of the guide arrangement tapering from the first end to the second end which is narrower than the first end, wherein an output path is provided through the second end at substantially the centre of the guide arrangement; an activation arrangement; and a delivery arrangement which is configured, in response to triggering of the activation arrangement, to deliver a quantity of the marking substance from the body, along the output path and out of the second end, wherein, in use, a user inserts at least the second end of the guide arrangement into an aperture in an element positioned adjacent a surface until the outer surface of the guide arrangement contacts the aperture, and the user triggers the activation arrangement to deliver a quantity of the marking substance through the second end and onto the surface to mark the surface at a position which is substantially aligned with the centre of the aperture.