Two-body resonance angles over time of an isolated nonresonant HR 8799 system that is near MMR, starting with the inner planet pair (HR 8799 e and HR 8799 d) and ending with the outer planet pair (HR 8799 c and HR 8799 b). The colours show the use of the argument of pericentre of either the inner planet (blue) or the outer planet (orange). The plots show that the planets are near MMR as the resonance angles are librating. These arguments of pericentre are noisier towards the outer planets as these planets have lower eccentricities. Therefore, the argument of pericentre is more sensitive to change and becomes harder to determine.