Ratio of the distance travelled by the centre of the spot to the distance simultaneously travelled by the mobile phase: \[R_{\text{F}}=\frac{b}{a}\] By definition the R F values are always less than unity. They are usually given to two decimal places. In order to simplify this presentation the hRF values may be used: they correspond to the R F values multiplied by 100. Ideally, R F values are identical to the R values used in column chromatography.