Up to now, the transfer functions shown have been for ideal converters. However, in the real world there are error sources in converters, which result in a non-ideal transfer function. Let’s look first at two sources of linear error, offset and gain. The effect of the offset error is to shift the entire transfer function either up or down (the example shown is for moving the transfer function up, representing a positive offset error). The offset error shifts every code of the converter by an equal amount. Therefore, if the converter has an offset of +2LSB, each analog value will be shifted by +2LSB from the ideal.  Note that in a unipolar converter the offset error and the zero error are identical. This is not always the case in bipolar converters.