I got this to work using the following style:

<Setter Property="ToolTip">
<Setter.Value>
<MultiBinding Converter="{StaticResource CellValueHistoryConverter}" StringFormat="Old Value: {0}">
<Binding RelativeSource="{RelativeSource Mode=Self}" Path="Field"/>
<Binding RelativeSource="{RelativeSource Mode=Self}" Path="Record"/>
</MultiBinding>
</Setter.Value>
</Setter>

And the following converter:

public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
if (values == null || values.Length != 2) return null;

var field = values[0] as Field;
var record = values[1] as DataRecord;
if (record == null || field == null) return null;

var dataHistory = record.GetDataValueHistory(field);
var lastItem = (dataHistory == null) ? null : dataHistory.Last();
return lastItem == null ? null : lastItem.Value;
}

Is this the suggested way to do this or do I have other options?  By the way, my string format is still not showing up - I had to add it to my converter

Hello Javier,

Thank you for your post.  

I have been looking into it. I am glad that you have managed to resolve your first issue. About your requirement for StringFormat, what I can suggest is to add the string that you want to display before cell`s value directly in your converter. I created a short sample  application based on your scenario to show you how you can implement this. If you are not able to reproduce the issue with the attached sample application, would you please modify it with the functionality, that you are using, so it reproduces the issue. This way I would be able to further investigate this for you and provide you with more detailed information on this matter.  Please let me know if I am missing something about your scenario.

Please let me know if you need any further assistance on the matter.

Hey Nikolov,

Thank you for your response.  It seems your demo is very similar to my approach - I was able to resolve both my issues with the code I posted last night.  I was wondering if there's a better way to go about getting the initial value of a cell?

Is there a better way to go around getting the initial value of a cell?

?

Hello Amilcar,

Thank you for your feedback.

Please let me know if you need any further assistance on the matter.

Thanks for the insight; I decided to keep my approach as it is working fine.  I was just wondering if there's a better more standard way to do it.

Hello Amilcar,

I am just checking your progress on the issue that you are having.

If you require any further assistance please do not hesitate to ask.

Hello Amilcar,

Thank you for your feedback.

I have been investigating your question and contacting with our development team.  DataValueChanged feature could be helpful in your scenario only if you know in advance that the number of changes that you will make,  will be small, since the control keeps the last ‘n’ of number changes in memory. There is  no reliable  a way to set ‘n’ to a value that ensures the initial value will be preserved in the history and that the history will not grow to a point where memory consumption becomes an issue. If you only want only to tracking changes that the user makes via editing cells, another available  approach is to use the Tag property of the Cell, so you could handle  the EditModeStarted event. If the Tag property of the Cell is null then get the value and set it on the Tag property and bind your Tooltip to this Tag property.

Please let me know if you need any further assistance on the matter.