In order to eliminate these accidental features from the situation, it is customary for bond-dealers to classify bonds purely on the basis of their yield, or net income return. As a thorough understanding of this point is essential to an accurate judgment of bond values, whether railroad bonds or otherwise, it must be developed in detail, even at the risk of carrying the reader over familiar ground. If a bond sells above par, it does not yield its purchaser a net return as great as the rate of interest which the bond bears, for two reasons: first, because the loss in principal, represented by the premium which the purchaser pays, must be distributed over the number of years which the bond has to run, and operates to reduce the rate of interest which the holder receives; and, secondly, because the rate is paid only on the par value of the bond instead of on the actual money invested. Thus, if a 6-percent bond with eight years to run sells at 110-3/4, it will yield only 4.40 per cent, which means that if the holder spends more than $48.73 (4.40 per cent of $1,107.50) out of the $60 which he receives annually, he is spending the excess out of principal, and not out of income. Conversely, if a bond sells below par, it yields more than the rate of interest which the bond bears. These yields have been calculated with the utmost exactness for all bonds paying from 2 per cent to 7 per cent and running from six months to one hundred years, so that it is only necessary to turn to the tables to discover what will be the net return upon a given bond at a given price. This net return is generally known as the "basis," and bonds are spoken of as selling upon a 3.80 per cent basis or a 4.65 per cent basis or whatever the figure may be, with no reference whatever to the price or to the rate of interest which the bond bears. Indeed, so exclusively is the basis considered by bond-dealers that very often bonds are bought and sold upon a basis price, and the actual figures at which the bonds change hands are not determined until after the transaction is concluded. It is not expected, of course, that the average business man will purchase bonds in quite as scientific a way as this, but it is essential that he should understand that while the intrinsic value of a bond is determined only by the five general factors described, its money value, or price, is affected also by these two accidental conditions. Exprest in other words, he must realize that the general factor described as _rate of income_ does not mean the coupon rate of interest which the bond bears, but the scientific "basis," derived by elimination of the accidental features.