because I'm either misunderstanding how to read a simple graph, or multiple companys' examples online all have the same typo.

The following is a 2 page pdf of a pretty basic set of graphs. There's even an example on page 2 of how to calculate a value using the graphs.

http://products.coltonind.com/Asset/108_STR990-1_Pressure-Drop-Data-Y.pdf

Here's the thing. The example is for 1-1/4" and 30GPM. So you follow 30GPM up til you hit the 1-1/4" line, then follow to the left to get the pressure drop, which would be 2.2ish, right?? Well, according to the answer to the example, WRONG! It says the answer is 1.0 psid. You'll notice, though, that the 1-1/2" line lands exactly on 1.0 psid at 30GPM, and the 1-1/4" line lands exactly on 1.0 psid at 20GPM. Either one would be correct in this instance, which would lead one to believe that it's a typo, either that they mean 1-1/2" at 30GPM, or 1-1/4" at 20GPM.

But here's the crazy thing. This isn't the only company's data sheet that uses the EXACT same example!

Page 21/22 of this PDF from a different company entirely gives the same graph and example:

https://www.islipflowcontrols.com/files/literature/cast-y-strainers.pdf

And I know I'm not reading this type of chart incorrectly, because I've found multiple other companys' data sheets in which their examples actually match! F.ex.:
Page 15 on:
https://fischer-robertson.com/pdfs/manufacturers/fil-trek/DataSheet%20-%20Fabricated%20Elbow%20Style%20Y%20Strainer%2095%20Series.pdf

Page 5 on:
https://www.mtncom.net/store-files/spec-sheets/Apollo%20Valves/Strainers/125YF%20250YF%20Flg%20Y-strainers.pdf

Both of these have different values in their respective examples of how to read this type of chart, and I come to the value they come to!

So was there a typo that was replicated on multiple companys' documentation, or am I crazy / still missing something???