A user defined reponse spectrum is always a relative spectrum with values between 0 and 1. It is scaled to the correct size with the reference acceleration and reference peroid (see example).

## Example

- Assume we have this design spectrum in Excel. Column A contains the period T in [s] and column B contains the design accelaration S
_{d}in [g]. - Find the maximum value for the period T
_{max}in column A and the acceleration S_{d,max}in column B. - Select the cells containing the spectrum values,
**don’t select the labels**! Press`CTRL`+`C`. - Go to the the spectrum dialog in Diamonds.

Select the relevant direction U, V or W (the vertical direction W is only selectable when you check the option*Include vertical component*). Click on. Diamonds will transfer the spectrum to a relative spectrum and paste the values into the table. A relative spectrum means that- Column A will be divided by T
_{max} - Column B will be divided by S
_{d,max}

- Column A will be divided by T
- Set the reference period in Diamonds equal to T
_{max}from the Excel.

Set the reference acceleration equal to S_{d,max}from the Excel.**Mind the units! 1g = 9.81m/s² so****0.7454g equals 7.31 m/s²!**Define the displacement factor (q

_{d}in EN 1998-1-1 §4.3.4).

- We’ve now defined the spectrum in one horizontal direction.

Repeat the steps for the other horizontal (V) direction and the vertical (W) direction if necessary.