You *can* obtain the numeric value of an object that bears one, by asking for its "numericValue", which you'll find in the "basic" category of the object's Viewer.  (Unfortunately, some objects that can bear a numeric value, such as the "Number (bare)" and its confreres found in the Basic-1 category of the Objects catalog, are not set up for use with etoy -- see PS below.)

For example, in the "NumericValue" project (recently placed on the Squeakland BSS,) an arrow is scripted to move forward at a speed obtained from the "speed-slider" object and to turn by an amount obtained from the "angle-slider."  Here is a picture of the objects and scripts in this project:

Similarly, you can get and set the numericValue of any "text" object.   In the  "squarer" project, also just placed on the Squeakland BSS, the pink "its square" box is scripted to compute the square of the number you type in to the green box:

See also Diego Gomez Deck's beautiful "Spirograph" example, also on the Squeakland BSS.

Cheers,

  -- Scott

PS:  The "Basic-1" and "Basic-2" categories of the Objects catalog were added latterly to Squeak as part of an unfinished effort outside the framework of e-toys -- that's why none of the three "Number" objects found in Basic-1 has "numericValue" offered in its Viewer.  This should be fixed, or else these underpowered "Number" offerings should be removed from the Objects catalog.  For the time being, anyway, I suggest that people use texts and sliders to hold numbers they want to work with using etoys.  Alternatively, manually create a numeric instance variable for some object, and obtain a "watcher" for it from the object's viewer.