It seems that Chronos rounds NTSC frame rates. Mediainfo shows this:
Frame rate : 29.970 (29970/1000) FPS
Original frame rate : 29.970 (30000/1001) FPS
Frame rate : 59.940 (59940/1000) FPS
Original frame rate : 59.940 (60000/1001) FPS
The difference is marginal and has usually no practical impact, but does anything stand against using the precise values as target frame rate (i.e. 24000/1001, 30000/1001 and 60000/1001)?