Red dotted lines on cowling engine ??

[ROY]

HI,
Can someone tell me if the red dotted lines on the engine cowling markings have historical significance?
What do they correspond to? what do they mean? Are they useful for something?
Thank you for your information.

 

[Fifinella]

 

[ROY]

 

[43-29080]

 

[ROY]

 

[AOP]

 

[ROY]

 

[bob turner]

 

[43-29080]

 

[AOP]