REW Measurement repetitions greyed out

[AnthonyLoFi]

Afternoon all,
I am measuring a speaker and have found on the "make a measurement menu" under sweep and settings that the number to repetitions per each sweep is greyed out and can not be used?
I have used this excellent software for some time now and have never thought to do a number of sweeps to get a better average but tried today and .... hence this post.
I use a UMIK-1 on a Mac.
I have searched the site so hope Im not asking something that has already been answered.

 

[John Mulcahy]

Here's the relevant section from the help:

REW allows multiple sweeps to be averaged, although best results are generally obtained by using single, longer sweeps rather than multiple, shorter sweeps. Multiple sweeps are offered when not using a Timing reference or when using a loopback as a timing reference. Do not use multiple sweeps if the input and output are on different devices (for example, if the input is a USB mic).

Multiple sweeps are disabled when a USB mic is being used (since input and output will always be separate devices and time synchronisation will not be maintained), or when using the acoustic timing reference.

 

[AnthonyLoFi]

Thank you John.
Appreciated and will search the website in more stringent detail in the future.