Each task is estimated certain number of hours to complete. The actual number of hours consumed to complete the task is calculated.

Now I want to find out the variance between estimated time and actual time. I get #### when variance is negative value.

[TABLE="width: 225"]

<colgroup><col span="3"></colgroup><tbody>[TR]

[TD]

**Estimate**[/TD]

[TD]

**Actual**[/TD]

[TD]

**Variance +/-**[/TD]

[/TR]

[TR]

[TD]2:00:00[/TD]

[TD]8:00:00[/TD]

[TD="align: center"]##########[/TD]

[/TR]

[TR]

[TD]4:00:00[/TD]

[TD]8:30:00[/TD]

[TD="align: center"]##########[/TD]

[/TR]

[TR]

[TD]8:00:00[/TD]

[TD]6:00:00[/TD]

[TD]2:00:00[/TD]

[/TR]

[TR]

[TD]16:00:00[/TD]

[TD]3:00:00[/TD]

[TD]13:00:00[/TD]

[/TR]

[TR]

[TD]32:00:00[/TD]

[TD]1:00:00[/TD]

[TD]31:00:00[/TD]

[/TR]

</tbody>[/TABLE]

What is the formula to calculate variance and to show the negative value in hours?