I have a book called ספר הקריאה השלם: חלק ג, פיתוחי חותם. I bought it from my shul and don't have any other chalakim or further information on it. It's not a kids' book, but it looks like one (pages about the size of Little Midrash but only about 100 of them, big font, colorful picture on the cover).
On page 79, they talk about metagim, which are short vertical lines that act as secondary accents for the word. (NOT the sof pasuk lines, although those look the same. Also NOT the lines that siddurim put to indicate the primary accent on words where that is the last syllable.) See the blue letters here, except for the last blue letter of each pasuk which is a sof pasuk.
וראוי להזהר לקרות המתגים במקומן הראוי להן כי לפעמים משתנה הענין...וכיון שהמתג מורה על כוונת הענין לפעמים, על כן מחוייב להזהר בקראיתו ולהדגישו
And it's appropriate to be careful to read the metagim in their proper place because sometimes it changes the meaning of the word...and since the meteg sometimes tells you what the word means, therefore it is required to be careful when reading it and to emphasize it.
In the middle of the paragraph, where I put the ..., they give examples: זכרה and ויראו. I am not convinced that those are good examples. I understand that before some publishers started marking kamatz katan and sheva na the only written difference was the meteg, but the main audible differences are the sheva na vs. nach and kamatz rachav vs. katan/chirik malei vs. chaser.
- Is there any place where a meteg alone changes the meaning of a word?
- Assuming (1), is their argument correct? Because metagim sometimes change the meaning, you have to be careful even when they don't? And conversely, is it less important to be careful about a grammatical rule that never changes the meaning?