f the center text/value 
* @param {text=} text after center text/ value
* @param {text=} unit of the center value
* @param {text(false,true)=false} display a scale with values along the slider (optional, default='false')
* @param {value=20} scale-integer, the scale-divider for the scale
* @param {text=} icon to be displayed in the center (optional)
* @param {text(pie,quarter-top-left,quarter-top-right,quarter-bottom-left,quarter-bottom-right,half-top,half-bottom,half-left,half-right,custom-half,custom-quart