[NTG-context] Characters per inch with ConTexT

Hi, I am writing a document where the guidelines say that I should use Times Roman font at 10pt with 15 characters per inch and 6 lines per inch. I am using thermes from tex gyre rscaled=1.015 as the bodyfont. At this setting I get a bit more less than 6 lines per inch (which is fine) but roughtly 17 characters per inch. Any way I could setup fonts so that both these criteria is automatically met? Why do people come up with such criteria :(( Aditya