We have built many projects, and we believe the most valuable summary indicators are:

• Dτ = Delivery lead time. Product teams may say "from concept to customer" or "from idea to implementation".

• Dμ = Delivery service rate. Devops teams may say "deployment frequency" or "we ship X times per day".

• Dε = Delivery error ratio. Quality teams may say "change fail rate" or "percentage of rollbacks".

• Rτ = Restore lead time. Site reliability engineers may say "time to restore service" or "mean time to restore (MTTR)".

Queueing theory
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