eric48:
Such good data to play with! therefore, we should not spoil the party

This is an easy enough DIY, with a smartphone calculator, a piece of paper and a ruler; a spreadsheet would be handy since it has a build in linear regression capability (but you can do without); there may be some on-line tools as well.

In order to vizualize a trend, we need to plot against time... Plot what ?

On the X axis, I'd recommend time, in decimal month unit (a decimal month is the number of days elapsed divided by 30.5 or you can use 30);

Shortcut: 26th Apr is month 0; 09th Jul is month 2.42; 14th Oct is month 5.6; Jan 15 (2014) is 8.65

On the Y axis, I'd suggest to use the Log10 transform. What is the Log10? In case you don't know or remember, I'll let you find out... As far as I am concerned, it is printed on my lab reports. Just ask, you'll find many people here able to explain you what this is.

Why Log10 transform before fitting? here again, just ask, you'll find many people here able to explain why... Hint: first chapter(s) of any book on regression

Shortcut: VL : 98906 is Log10(VL) = 4.995 VL : 54748 is Log10(VL) = 4.738 VL : 29197 is Log10(VL) = 4.465

Pencil, paper, ruler (or use a pencil), draw and, then... comment.

Easy enough, right?

Need help? Just ask here and you'll find many people here able to help you