One critical restriction remains, however: the lack of available fonts. In the same way that a bureau usually requires a copy of a font in a document sent for print, so too must a Web surfer have your chosen fonts installed before type within your site will appear correctly. In practice, this restricts you to fonts common to Windows and Mac: Verdana, Trebuchet MS and Arial for sans serif; Georgia and Times New Roman for serif; Courier New for monospace; Arial Black, Impact and the inexplicably over-used Comic Sans MS for display type. Although it is possible to define ‘fall-back’ fonts (these are listed one after the other, separated by commas, and the browser moves to the next choice if the previous one isn’t installed), it is pointless to set a first choice that the vast majority of your audience will not see, so you will have to get used to these ‘Web-safe’ fonts. Note that, like images, Web fonts should be sized in pixels (or percentages), not measurements such as points and millimetres.