It seems there area always 5 gridlines, including the axis, and their
values are distributed evenly on the arithmetic scale. Thus if the max
gridline is 10^2, and min is 10^0, then on the arithmetic scale we get
2, 1.5, 1, 0.5, 0, corresponding to 100, 31.6, 10, 3.2, 1 on the log
scale.

However, I don't understand how the max and min gridline values are
determined. I guess the max value 1000 is the next round value that is
a power of 10. But how is the min gridline value 1.6 calculated?

On Aug 15, 2:53 pm, protovisuser <[email protected]> wrote:
> What is the algorithm for determining at what values the gridlines
> appear for a log scale?
>
> I tried the column chart in the playground using the following data:
>   var raw_data = [['Austria', 13,13,13,13,13,13],
>                   ['Bulgaria', 13,13,13,13,13,13],
>                   ['Denmark', 13,13,13,13,13,13],
>                   ['Greece', 6,13,13,13,13,584]];
>
>   var years = [2003, 2004, 2005, 2006, 2007, 2008];
>
> And using the following settings:
>     {title:"Yearly Coffee Consumption by Country",
>             width:600, height:400,
>             hAxis: {title: "Year"},
>             vAxis:{logScale:true}}
>
> The y-axis has the following gridlines:
> 1.6, 7.9, 39.8, 199.5, 1000
>
> How are these values calculated?

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