Inconsistent result of binary operation

[robpie]

Every execution of following query returns different results. 

go_memstats_alloc_bytes{instance="demo.robustperception.io:9090"} - go_memstats_gc_sys_bytes{instance="demo.robustperception.io:9090"}

Could you tell me why?

Try it here:

http://demo.robustperception.io:9090/new/graph?g0.expr=go_memstats_alloc_bytes%20-%20go_memstats_gc_sys_bytes%7Binstance%3D%22demo.robustperception.io%3A9090%22%7D&g0.tab=0&g0.stacked=0&g0.range_input=1h

Regards, 

R