Labeling number of trials

I have survey data from multiple sites that I visited repeatedly over the course of a month. What I am trying to do is label each date that a site was visited with a sample number. For example, if a site was visited on 3/1, 3/2, 3/4 and 3/10, I want each row of data from each of those dates to have a label with the sample number (1,2,3 and 4).

excel forum sample.xlsx

An example of my data is above. I want to create a new column (called "Sample Number"). For each row of data I want a label with the sample number. For example, A1 was sampled twice (on 4/29 and 5/26), and I would like these sample numbers to be labeled with "1" and "2" repeated down the "Sample Number" column across from their corresponding dates.

I hope that makes sense. I think I need to use an =IF statement, but I'm not sure how to proceed. Thanks for your time!

Best,
Lizzie

Thanks for the quick response! Unfortunately that did not work. I adjusted it, because at first it gave me an error, but after adjustment to this: =B2&COUNTIFS(A$2:A2,A2,B$2:B2,B2), I got the third column in the link.

excel forum sample.xlsx

What I actually want is what I manually entered in the third column. I have hundreds of rows of data, so entering manually isn't sustainable for me.

Again, thanks for the quick reply.

Best,
Lizzie

A1 is the site, and it was sampled on two different dates. The four letter codes are observation data collected at the site on the date.