The vertical pose rotation of armor stand arms pivot from the side of the arm, rather than its center.

Why is this an issue?

It overcomplicates map makers getting precise poses/positions/alignments with armor stands for visual use by offsetting the arm's pivot point.

Steps to reproduce:

Run commands:

In chat:

• /scoreboard objectives add pose dummy
• /summon armor_stand ~ ~ ~ {ShowArms:1b,Pose: {RightArm:[0f,0f,0f]}

  ,Tags:["pose"]}

Repeating:

1. /scoreboard players add pose pose 1
2. /execute store result entity @e[tag=pose,limit=1] Pose.RightArm[1] float 5 run scoreboard players get pose pose

Notice the arm rotates from the inner side of the arm's top, not its center.