Max top/base spread

[YoungEventer]

I'm probably being really dim but could someone explain to me what 'max top spread' and 'max base spread are referring to (What part of the jump) I've always thought spreads to be measure from the front to the back so the different sizes have gotten me all confused! Also is there a minimum width of fences eg. skinines? Thanks!

 

[millitiger]

Top spread- measuring front to back, highest point of the fence.

Base spread- measuring front to back at ground level of the fence.

 

[CrazyMare]

Something like this would have a similar top and base spread

While this has a smaller top spread to base spread