A Reference Card or "Romer" is a device for increasing the accuracy when reading a grid reference from a map. Made from transparent plastic, paper or other materials, they are also found on most baseplate compasses. Essentially, it is a specially marked-out ruler which matches the scale of the map in use. The scales are laid out in reverse, such that by lining up the numbers given in the grid reference with the gridlines for the square in question, the corner of the romer lies on the location whose grid reference you wish to read. Some transparent versions have a small hole at the origin when this is not at the corner of the Reference Card. This allows access to the map such that the location could be marked with a pencil if using the Reference Card in reverse having been given a grid reference to start with. They are used in many types of land navigation.

The Römer (German surname, "Roman") is a medieval building in the Altstadt of Frankfurt am Main, Germany, and one of the city's most important landmarks. The Römer is located opposite the Old St. Nicholas church and has been the city hall (Rathaus) of Frankfurt for over 600 years. The Römer merchant family sold it together with a second building, the Goldener Schwan (Golden Swan), to the city council on March 11, 1405 and it was converted for use as the city hall. The Haus Römer is actually the middle building of a set of three located in the Römerberg (a plaza).

Ole Christensen Rømer (; 25 September 1644 – 19 September 1710) was a Danish astronomer who in 1676 made the first quantitative measurements of the speed of light. In scientific literature alternative spellings such as "Roemer", "Römer", or "Romer" are common.