Each of the r i series has their own scale and range of retention index values. Therefore, these values are not directly comparable between the series. All compounds that had a higher or lower r i value for the corresponding range of the model it was coming from, were classified as 'maybe' inside the RPLC subspace, due to the fact that these chemicals either elute close to t 0 or require high percentages of organic eluent to be eluted.