I've uncovered some information about Carrol Romer of which this is a digest.
He was born in 1883 and read engineering at Cambridge. In 1905. in the glorious days of empire, he entered the Egyptian Survey Department. He then read law and was called to the Bar. In 1915 he was appointed Officer Commanding Maps and Printing Section of First Army Intelligence and was responsible for the surveying and revision of maps of trenches on the Western Front. He was also an expert at interpreting aerial photographs of German positions.
In January 1916 Temp. Lt. Carrol Romer was awarded the Military Cross (for two years after the MC was instituted it was awarded for for meritorious service as well as for bravery in action).
The maps used were at several scales and were printed with squares representing 1,000 yards. There is an illustration of a Reference Card, what we now call a romer, in the 1921 War Office Manual of Map Reading, Photo Reading and Field Sketching. It seems likely that the term was used colloquially in the War Office map department and was first used officially in the 1929 edition of the War Office Manual of Map Reading...which also contained instructions on how to make one from a piece of card.
After the war, Carrol had a distinguished career at the Bar and edited the important literary and philosophical monthly journal Nineteenth Century and After. In 1931 he was appointed Assistant Registrar, Court of Appeal, and later became King's Coroner and Attorney, Master of the Crown Office, and Registrar of the Court of Criminal Appeal. He died in 1951.
Sources: Sheetlines 63 & 64 (the journal of the Charles Close Society for the Study of Ordnance Survey Maps) which cites several original sources. It seems that some of this information can be found in Chasseaud, Peter, Artillery's Astrologers; a History of British Survey and Mapping on the Western Front 1914-1918, Mapbooks, 1999 (I've not seen a copy).
Hugh