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# Why Error Checking is Important

3:04 with Tyler TallonNow let's learn about the importance of error checking and look at some effective ways to check your work.

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Please note that **this is a new spreadsheet**, different from the one you used in the previous stage:

[MUSIC]
0:00

So far in this course we've learned
how to use look up functions,
0:09

create a pivot table, and learned how
to use several other tools in Excel.
0:13

Now we're going to learn about
the importance of error checking,
0:17

which has saved me so many times.
0:20

And I'm excited to show you some
effective ways to check your work.
0:22

Before we dive in to
the error checking process,
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let's first discuss some
common errors in Excel.
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Generally, there are four
different types of errors.
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Input errors, which are data
entry errors or missed data.
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Output errors, usually caused by incorrect
cell referencing, problems with time or
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date switches or
graphic outputs not updating properly.
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Conceptual logic or
using the wrong formula.
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And then formula errors, which could
be using the correct formula but
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typing it incorrectly,
or the wrong order, or
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incorrect parenthesis,
basically just bad math.
0:58

Let's drill down a little further on
some of these errors by looking at
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a few examples on our spreadsheet.
1:04

First, let's look at a common error
that can come from adding rows.
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Here we have store sales by state in
month for the first half of the year.
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Let's say we want to say a sum
to get the total at the bottom.
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Let's sum each month by using
the AutoSum feature up at the top right.
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And then let's copy this over for
each month.
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Okay, now let's add a row to our data.
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For newer worksheet versions
like I'm using, if you add
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a row in the middle of your data, then
the sum range will automatically update.
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You can see this by double
clicking on the sum row, and
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a box will appear around the group
of cells that it's summing.
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It's always good to double
check this when you add rows.
1:51

But now let's try adding a row at the top.
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If I add a row here, And
then double-click on this sum row,
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you'll notice that the top row
is not included in my sum.
2:03

So if I were adding data for Alabama here,
2:07

You'll see it's not included in the sum.
2:26

To correct this, you can just change
the formula to start at B2 instead of B3.
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Now you can see it's
including every state.
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And then you'll want to make sure to copy
that formula over to the remaining months.
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Now just to make sure it copied correctly,
let's double-click on June's total.
2:52

Yep, looks like I copied over correctly.
2:57

Coming up, we'll keep looking
at some common errors and
3:00

learn about how to avoid them.
3:02

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