Strutt sheets display the preferred band centre frequencies at the top of each Strutt sheet (e.g. 31.5 Hz, 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz & 8 kHz on a 1/1 octave band sheet).
However, Strutt functions generally use the exact band centre frequencies when performing calculations.
You can use the Strutt "ISO Bandwidths" userform (located on the "Fundamentals" drop-down menu) to view the exact centre frequencies (see Figure 1).
It is possible to use the preferred centre frequencies in many Strutt functions, if you wish.
For example, in Figure 2, changing the last parameter in the dBA() function from TRUE to FALSE causes the function to use the preferred octave band centre frequencies in the calculation.
Note that using the preferred centre frequencies makes a negligible difference to the resulting dB(A) rating.