SLI

A = http_response_5xx
B = http_response_total
SLI = asPercent(diffSeries(#B,#A),#B)

Budget

A = http_response_5xx
B = http_response_total
C = diffSeries(#B, scale(#B,0.9995))
Budget = integral(#C)
Spent Budget = integral(#A)