Why isn't 0?

[leezhihong]

In the pivot table, the negative number is "-21.919", and the positive number is "21.919", so in the sum should be 0.
Why is "1.77636E-15"?

1.data

<b>???</b>

Excel Workbook
	A	B	C	D	E	F	G	H	I	J	K
3	??	????	??	??	???????	????	??	??	??	???	??
4	2011-4-5	??	???	???????	??HRB335?16*12	1710869		17	0.322
5	2011-4-5	??	???	???????	??HRB335?16	1710869		33	0.469
6	2011-4-5	??	??2?	????	??Q235?10	1002289	-3		-4.597
7	2011-4-5	??	??2?	????	??HRB335?25	1002289		-64	-2.221
8	2011-4-5	??	??2?	????	??HRB335?28*12	1002289		-61	-3.541
9	2011-4-5	??	??2?	????	??HRB335?12	1002289		-493	-3.942
10	2011-4-5	??	??2?	????	??HRB335?22	1002289		-254	-6.827
11	2011-4-5	??	??2?	????	??HRB335?16*12	1002289		-17	-0.322
12	2011-4-5	??	??2?	????	??HRB335?16	1002289		-33	-0.469
13	2011-4-5	??	2#??	2#??	??Q235?10	1002289	2		3.062
14	2011-4-5	??	2#??	2#??	??HRB335?25	1002289		64	2.221
15	2011-4-5	??	2#??	2#??	??HRB335?28*12	1002289		61	3.541
16	2011-4-5	??	2#??	2#??	??HRB335?12	1002289		493	3.942
17	2011-4-5	??	2#??	2#??	??HRB335?22	1002289		254	6.827
18	2011-4-5	??	2#??	????	??Q235?10	1710868	1		1.535
Sheet

2.Pivot Table

Excel Workbook
	A	B	C	D	E	F	G	H
3	??	????	??	???????	??	??	???	??
4	2011-4-5	??	??2?	??Q235?10	-3		1.532	-4.597
5				??HRB335?28*12		-61	#DIV/0!	-3.541
6				??HRB335?25		-64	#DIV/0!	-2.221
7				??HRB335?22		-254	#DIV/0!	-6.827
8				??HRB335?16*12		-17	#DIV/0!	-0.322
9				??HRB335?16		-33	#DIV/0!	-0.469
10				??HRB335?12		-493	#DIV/0!	-3.942
11			??2? ??		-3	-922	7.306	-21.919
12		?? ??			-3	-922	7.306	-21.919
13		??	???	??HRB335?16*12		17	#DIV/0!	0.322
14				??HRB335?16		33	#DIV/0!	0.469
15			??? ??			50	#DIV/0!	0.791
16			2#??	??Q235?10	3		1.532	4.597
17				??HRB335?28*12		61	#DIV/0!	3.541
18				??HRB335?25		64	#DIV/0!	2.221
19				??HRB335?22		254	#DIV/0!	6.827
20				??HRB335?12		493	#DIV/0!	3.942
21			2#?? ??		3	872	7.043	21.128
22		?? ??			3	922	7.306	21.919
23	??				0	0	#DIV/0!	1.77636E-15
pivot

 

[Derek Brown]

This will be down to the 'precision' problem that some calculations encounter.
More information about precision:
http://www.cpearson.com/excel/rounding.htm
If the values that you gave are those being 'displayed' then the real values may have more decimal places. Rounding those values may help.

 

[leezhihong]

Thank you, Derek Brown!