t-Tests and p-Values

I'm writing a guide for students using Excel in a lab course, and I've run into a little problem regarding consistency in Excel. When I run a t-test in the Data Analysis tool, I get a different result than if I use the =t.test function. The Data Analysis tool yields a p-value of 0.4631, while the t.test function gives me 0.4624. I made sure that I used the same settings for both (two-tailed, unequal variances). I also hand-calculated the degrees of freedom for the test, and it should be 11.46 or so, and the Data Analysis output yields 11, so I suspect that the function floats the degrees of freedom, while the tool approximates it to a whole number.

I'm not sure, though, and I wanted to make sure I don't tell the students to do something wrong. To anyone who considers this problem, thank you.

You can find the whole file here.