I'm not sure why one end is black, and one has the tip cut off, but either end will work, although you may need to either read the numbers upside down, or count backwards. Please let me know if you know more about this than I do, and can explain these things!
Anyway, I'll demo the 2 1/2" option, which uses 2 1/2" strips, to give you 2" finished triangle squares.
(please forgive the blur and glare - still inept at taking photos)
Next, lay your ruler tip side down alongside your marked line, as shown
Then use the Easy Angle to mark your line.
Now sew 1/4" from each side of the line, and cut apart.
Open and press...