How to control the speed of a rotation

Actually I use the SVG to send into an ilda Laser so the code is :

ildaFrame.getPolys().clear();
polylines.clear();
ofPolyline p;
while (svgLoader.hasNextPolyline()){
    p.clear();
    p = svgLoader.getPolyline();
    // size and rot
    for (int i=0; i<p.size(); i++) {
        ofVec2f pt = p[i];
        pt.x *= 2.;
        pt.x -= 1.;
        pt.y *= 2.;
        pt.y -= 1.;
        
        pt *= size;
        pt.rotate(whichRot);
     
        p[i] = pos+pt;
    }
    polylines.push_back(p);
 svgLoader.update();
}

and the rotation :

 whichRot=rotation; 
 rotation = ofGetElapsedTimef()*100*rotationSpeed;

Cyril