A screened subnet is a network segment that separates two different environments, such as ОТ (operational technology) and IT (information technology), and provides security controls to limit and monitor the traffic between them. This would allow the business to get the required reports from the historian server without exposing the ОТ environment to unnecessary risks. Using a VPN, allowing IT traffic, or allowing PLCs to send data are less secure options that could compromise the ОТ environment. Verified References: https://www.comptia.org/blog/what-is-operational-technology https://partners.comptia.org/docs/default-source/resources/casp-content-guide