I have a table in which the column "Doc. No." has duplicate info as below; please advise on which formula I should use to count the number of unique Doc. that I have (as reference to the below table extraction for instance; at one glance we are able to determine that the number of Doc. is four, i.e. `21571`

, `27868`

, `25016`

& `21574`

).

However, my table has thousands of rows; therefore, doing this by eye is not feasible. Please teach me how to create the formula. By the way, I’m currently using Microsoft Excel 2010.

```
ROW No. DOC. No. DESCRIPTION
1 21571 COVERALL , RED SIZE : S
2 21571 COVERALL , RED SIZE : M
3 21571 COVERALL , RED SIZE : L
4 21571 COVERALL , RED SIZE : XL
5 27868 HOLLOW 4"X4"X6MMX6MTR
6 27868 HOLLOW 3"X3"X6MMX6MTR
7 27868 HOLLOW 2"X2"X61.6MMX6MTR
8 25016 DUCORIT/1000KG PER BAG
9 25016 DUCORIT/300KG PER BAG
10 21574 HW-045133, 4"X1/4"X5/8" 4" GRINC
12 21574 HW-055238, 5"X1/8"X7/8"5" GRINDING DISC
```