The spectrum data consists of pairs of values which are Period vs. Accn. or Period vs. Displacement. The acceleration or displacement values that you obtain from the geological data for that site may have been provided to you as normalized values or un-normalized values. Normalization means that the values of acceleration or displacement have been divided by a number (called normalization factor) which represents some reference value. One of the commonly used normalization factors is 'g', the acceleration due to gravity.
If the spectrum data you specify in STAAD is a normalized spectrum data, you should provide the NORMALIZATION FACTOR as the SCALE FACTOR. If your spectrum data is un-normalized, there is no need to provide a scale factor(Another way of putting it is that if you provide un-normalized spectrum values, the scale factor is 1, which happens to be the default value also.) Make sure that the value you provide for the SCALE FACTOR is in accordance with the length units you have specified. (A common error is that if the scale factor is 'g', users erroneously provide 32.2 when the length unit is in INCHES.)
STAAD will multiply the spectral acceleration or spectral displacement values by the scale factor. Hence, if you provide a normalized acceleration value of 0.5 and a scale factor of 386.4 inch/sq.sec., it has the same effect as providing an un-normalized acceleration value of 193.2 inch/sq.sec. and a scale factor of 1.0.