It is supposed to be that the upper number is the number of beats per measure, and the lower number is the note value that gets the beat.
4/4 is 4 beats per measure, where a quarter note is the beat, giving 4 quarter notes per measure.
6/8 is 6 beats per measure, where each beat is one eighth note, giving 6 eighth notes per measure.
Etc.
BUT, Sonar's Step Sequencer doesn't know a thing about any beat value (bottom number) than a quarter note, and THAT is why tempo has to get doubled if you want to switch between measures of 3/4 or 4/4, and measures of anything with an eighth note base, like 5/8, 6/8, 9/8.
Bob Bone