defines values for the vertical axis
webix.ui({
    view:"chart",
    type:"bar",
    value:"#sales#",
    label:"#year#",
    ...
});
As a function, the property accepts a data object and is called for each data item:
webix.ui({
    view:"chart",
    value:"#sales#",
    ...
})
//is equal to
webix.ui({
    view:"chart",
    value:function(obj){ return obj.sales; },
    ...
})
For multilevel charts, the value of parent items will be calculated automatically if it is not set in the initial structure.