Hi

I'm not sure if this is the right place to ask this,

but

In my grammar books, the Qal Perfect 3cp for a strong root like Shamar - Is Shin with Kamatz, Mem with Shwa, Reish, Waw with shurook. Note the Mem with Shwa.

In Numbers 9:23 Shin Mem Reish Waw appears, and both bible desktop and my OT parsing guide, say it's Kal perfect 3cp.

But instead of what i'd expect which is what the grammar books say for shamar in the qal perfect 3cp

The word in the tenach Numbers 9:23 is not Shamru, it's Shamaru. Shin kamatz, Mem kamatz, reish shurook.

My grammar book doesn't cover Mem Kamatz, as a form of Kal perfect 3cp

What am I missing here regarding the gammar of the kal perfect?