An objective test is one that has been tried out on a proper sample of the population for whom it is intended and that on this sample it has been shown to work I.e. to be both reliable and valid. It is usually made up of items each of which is discrete in itself and shown to contribute to the total performance of the test.
Items are linguistically meaningful.
By converting to z scores, it is possible to obtain equal units of measurement despite the fact that the original units of measurement were quite different. In an IQ test, the MEAN is set at 100 instead of zero as in z score. This allows positive numbers for scores either above or below the mean.