The best practice in PLC programming and control design is if the memory address is preceded by an “I” try not to use channel “1” for your input card to avoid “I1” in addressing. Likewise, but rare, if the memory address is preceded by an “O” try not to use channel “0” for your output card to avoid “O0” in addressing. With fixed I/O the latter is often un-avoidable, short of adding on extension slot so you can have O:1 memory address (with Siemens real world outputs are preceded with a “Q” so not really an issue. But with some fonts the letter I and the number 1 are barely distinguishable. Same with letter O and number 0. A typo or confusion could cost thousands in downtime, which is yet another distinction between computer programming and PLC programming.