The Circle object

<script>
    line = new RGraph.Line({
        id: 'cvs',
        data: [4,9,1,3,2,6,5],
        options: {
            spline: true,
            backgroundGridVlines:false,
            backgroundGridBorder:false,
            xaxis: false,
            yaxis: false,
            xaxisLabels: ['Monday','Tuesday','Wednesday','Thursday','Friday','Saturday','Sunday'],
            marginInner: 5,
            tickmarksStyle: 'endcircle',
            tickmarksSize: 10,
            colors: ['black'],
            textSize: 16
        }
    }).draw();

    x      = line.coords[2][0];
    y      = line.coords[2][1];
    radius = 15;

    new RGraph.Drawing.Circle({
        id: 'cvs',
        x: x,
        y: y,
        radius: radius,
        options: {
            colorsStroke: 'black',
            colorsFill: 'rgba(255,0,0,0.7)',
            tooltips: ['<b>Example</b><br />This is an example tooltip'],
            shadow: true,
            shadowOffsetx: 0,
            shadowOffsety: 0,
            shadowBlur: 5,
            textSize: 14
        }
    }).draw();
</script>

colorsStroke
The color used to stroke the circle.
Default: transparent

colorsFill
The color used to fill the circle.
Default: red

shadow
This controls whether the shadow is enabled or not.
Default: false

shadowColor
The color of the shadow.
Default: gray

shadowOffsetx
The X offset that the shadow is drawn at.
Default: 3

shadowOffsety
The Y offset that the shadow is drawn at.
Default: 3

shadowBlur
The severity of the shadow blur.
Default: 3

tooltipsFormattedListItems: [
    ['Bill','Jerry','Berty'], // First tooltip
    ['Gill','Carrie','Lucy'], // Second tooltip
    ['Pob','Nobby','Hilda']   // Third tooltip
]

.RGraph_tooltip ul#rgraph_formatted_tooltips_list li {
    text-align: left;
    color: yellow;
}

tooltips: {
    borderLeft: 'gray 2px solid',
    borderBottom: 'gray 2px solid'
}

tooltipsCss: {
    fontFamily: 'Verdana',
    fontSize: '20pt'
}

tooltips
The tooltip for the circle. Even though you can only have one - this should still be an array: obj.set('tooltips', ['The tooltip']);
Default: null

tooltipsEvent
This can be click or mousemove and controls what event is used to trigger the tooltip.
Default: onclick

tooltipsHighlight
This stipulates whether the circle will be highlighted when the tooltip is shown.
Default: true

tooltipsNohideonclear
Not an option that you'll need particularly often if at all. Setting this to true means that when you call the RGraph.clear api function the tooltip DOES NOT get hidden.
Default: false

tooltipsFormattedPoint
When using formatted tooltip strings this is used as the point when using the %{value_formatted} option.
Default: .

tooltipsFormattedThousand
When using formatted tooltip strings this is used as the thousand separator when using the %{value_formatted} option.
Default: ,

tooltipsFormattedDecimals
When using formatted tooltip strings this specifies the number of decimals when using the %{value_formatted} option.
Default: 0

tooltipsFormattedUnitsPre
When using formatted tooltip strings these units are prepended to the number when using the %{value_formatted} option.
Default: (an empty string)

tooltipsFormattedUnitsPost
When using formatted tooltip strings these units are appended to the number when using the %{value_formatted} option.
Default: (an empty string)

tooltipsFormattedListType
With this property you can switch between an unordered list (the default) and an ordered list. Possible values are ul and ol.
Default: ul

tooltipsFormattedListItems
This should be a two-dimensional array of the list items that are to be shown for all of the tooltips. An example of this property is:

tooltipsFormattedListItems: [
    ['Bill','Jerry','Berty'], // First tooltip
    ['Gill','Carrie','Lucy'], // Second tooltip
    ['Pob','Nobby','Hilda']   // Third tooltip
]

You can use css to style this list - for example:

.RGraph_tooltip ul#rgraph_formatted_tooltips_list li {
    text-align: left;
    color: yellow;
}

Default: null

tooltipsFormattedTableHeaders
When showing a table in the tooltips this can be an array of headers for the table. These are added to the tooltip using th tags.
Default: null

tooltipsFormattedTableData
This is the data that is added to the table. This is a 3-dimensional array so it's easy to make a mistake. See the example, copy the code from it and then modify it suit. You'll create fewer bugs this way.
Default: null)

tooltipsPointer
By default the tooltips have a small triangular pointer that points to the shape that was clicked on. You can turn this off with this property.
Default: true

tooltipsPointerCss
If you want any css values applied to the tooltips pointer (a css border, for example) then specify an object containing those values to this property. For example:

tooltips: {
    borderLeft: 'gray 2px solid',
    borderBottom: 'gray 2px solid'
}

Default: null

tooltipsPointerOffsetx
This allows you to adjust the vertical position of the tooltips pointer.
Default: 0

tooltipsPointerOffsety
This allows you to adjust the vertical position of the tooltips pointer (for example, if you add a border you may need to move it down slightly).
Default: 0

tooltipsPositionStatic
The new default (as of August 2020) is for tooltips to be positioned statically and not be dependent on the mouse position. If you don't want this for whatever reason, you can disable it with this setting. When you set it to false tooltips are positioned next to the mouse pointer.
Default: true

tooltipsCss
If you want to specify some css that gets applied to all of the tooltips, but don't want to use the RGraph.tooltips.style object (which gets applied to all of the tooltips on the page for every chart) you can use this property to give some per-object css for the tooltips. These are css styles that get applied to all of the tooltips for the specific object only. It should look like this:

tooltipsCss: {
    fontFamily: 'Verdana',
    fontSize: '20pt'
}

Default: null

tooltipsOffsetx
This property allows you to shift the tooltips left or right.
Default: 0

tooltipsOffsety
This property allows you to shift the tooltips up or down.
Default: 0

<div style="margin-left: 50px; display: inline-block">
    <canvas id="cvs" width="650" height="250"></canvas>
</div>

textAccessible
A new feature in 2016 that allows you to use dom text in place of canvas text. It makes for much higher quality text that you can also select if desired (for copy/paste operations). It won't fit all situations and you can read more about the DOM text feature here. A good way to control borders/margins/padding etc is not to set them on the canvas but to wrap the canvas in a div and set them on that like this:

<div style="margin-left: 50px; display: inline-block">
    <canvas id="cvs" width="650" height="250"></canvas>
</div>

Default: false

text
This allows you to add custom text to your chart if you want to. There's a dedicated page that describes this option here.
Default: null

highlightStyle
By default this is null but you can set it to a function if you wish so that function is called to do the highlighting. It's passed the shape object as an argument.
Default: null

highlightStroke
This is the color that the circle is highlighted (the stroke) in when the tooltip is shown.
Default: black

highlightFill
This is the color that the circle is highlighted in (the fill) when the tooltip is shown.
Default: rgba(255,255,255,0.7)

linewidth
This is the linewidth that is used when stroking the circle.
Default: 2

<script>
    circle.canvas.onclick = function (e)
    {
        RGraph.redraw();
    
        var canvas = e.target,
            obj    = canvas.__object__,
            shape  = obj.getShape(e);

        if (shape) {            
            // Highlight the main body of the Background object.
            obj.path(
                'lw 10 b a % % % 0 6.29 false s black f red',
                shape.x, shape.y, shape.radius
            );
        }
    }
</script>

obj.on('draw', function (obj)
{
    // Put your event code here
});

var obj = new RGraph.Drawing.Circle({
    id: 'cvs',
}).on('draw', function (obj)
{
    // Put your draw event code here

}).on('click', function (e, shape)
{
    // Handle the click event

}).draw();