置(お)きにRepeated at intervals, Every other, Every, At intervals of

Caution

It is very common to get ごとに and おきに mixed up. The former literally means 'every'. However, the latter having the meaning of 'at intervals' makes things confusing. おきに itself will only mean 'every' sometimes. Let's look at some examples of when these two expressions overlap in meaning, and when they do not.

Large time frames or distances - Only ごとに will be used to express 'every'. It makes sense to ask 'at what point' during a day, a week, or a month. Due to this, only おきに will mean 'after the interval of (A)', while ごとに means 'every'.

Small time frames or distances - Both ごとに and おきに may be used to express 'every'. It doesn't make sense to care about 'at what point' during seconds, minutes, or hours. Here, because おきに points at the interval, it will mean 'every interval of one second' etc, because nobody is going to ask 'when did (B) happen during the next second', so the space is just assumed to be 'one second'.

In summary, おきに will mean 'every (A)' for seconds, minutes, hours, millimeters, centimeters, and kilometers. But it will mean 'with spaces of' for almost anything bigger than that. This is not an exception to the rule, it is just a change of focus as spaces get larger. We can just remember that おきに always has one job. It highlights that (B) occurs after or outside of (A). While ごとに highlights (B) happening within (A).

一秒(いちびょう)おきに - The space is 'one second', so if おきに points to the beginning of the next second, the space is still only 'one second'. Because おきに doesn't care about where (B) happens within that next second, we assume straight away.

五年(ごねん)おきに - The space is 'five years', so if おきに points to the beginning of the next year, the space becomes 'six years', because we are going to want to know where (B) happens within that next year. It would be strange to assume someone is waiting for New Year of the sixth year to do something instantly.