Help with taking pictures

[RecessedCel5]

I need help taking pictures. everytime i take a picture at different distances (arm's length vs 1 meter), any ratio that involves width keeps changing.
How can i take the most accurate picture possible. i want to calculate my ratios

 

[CEO]

Bumped for you brother, good guy on here. Help a nigga out.

 

[RecessedCel5]

should i just get a CBCT scan ?

 

[Cordlet]

just do arms length out or a pic of u in the mirror. any closer than arms length gives lens distortion.