How percent_diff () query is working in grafana

Dear Team,

Awaiting for your reply and support. Below are the two sample values of percentage difference. please let me know, how grafana is conevrting into the percentage difference value.

1:Array[59.165783884444444,1587963600000]

2:Array[111.8284890311111,1587964500000]

Regards
Arjun