Back in Elementary School, when we were learning to add and subtract on a number line, it didn’t work for me. I kept puzzling over it. I asked the teacher about it, if it mattered if you counted spaces or lines, and she said no, but I couldn’t help seeing that there were more lines than spaces, or more spaces than lines, depending on if the number was even or odd.
Every once in a while, I’ll be counting stitches on my knitting, or counting inches as I measure a length of cloth, and things are off by one. This has left me a very nervous counter. I take forever casting on knitting projects because I have to count the stitches 3-4 times to be sure I did it right, preferably with a notepad and pencil to make tick marks.
Turns out, I am not losing my mind – this is a common problem people have, sometimes called “The fencepost error,” it has its own wikipedia page:
https://en.wikipedia.org/wiki/Off-by-one_error
If you find yourself off by one, chances are you’ve fallen into the fencepost error. Go back and start at the end of the first unit. Be consistent. (Oh how that word, consistent, terrifies me. Like I can never pick my finger up from the stitch it holds down as zero.)
Long story short: It DOES make a difference if you are counting spaces or lines. Take that, first grade teacher!
