Phijel

the set message isn't working whith the multislider (with only 1 slider here)

I must be missing something obvious here 

set-value-of-a-multislider-without-outputting-it

use the message [set $1], this will cause the slider to scroll if you mouse-scroll the number box though; i cannot see why your [prepend set] isn't working

[set slid_num slid_value] in general, [set 1 $1] in this case:

thanks Brendan, but it doesn't solve my problem.

May I remind you I'm using a multislider here (with one slider), not a slider

In fact I found the cause, in case of a multislider you have to address specifically the slider before giving its value, in form of a list

May I remind you I'm using a multislider here (with one slider), not a slider
In fact I found the cause, in case of a multislider you have to address specifically the slider before giving its value, in form of a list 

oops, i missed the 'multislider' part of your question

Set value of a multislider without outputting it