OB1 is in every programme as this is a main processing block

(like function main() in C or class main in Java).

if you use time processed block only (called at strictly fixed interval i.e. OB35 include -R col

at end of that OB35 block).

I use 'global' data block for all global variables and have there section Clock for free-running clocks, time after PLC startup, etc. and markers are used strictly for testing / commissioning purporses. this way I can find and remove testing code very quickly and global data can be nicely structured.