Related Rule
Practice Relating to Rule 15. The Principle of Precautions in Attack
Section D. Information required for deciding upon precautions in attack
Sweden’s IHL Manual (1991) states that the obligations to take precautions in attack “apply only as far as available resources for collection and processing of information permit”. The manual adds:
A planning commander must, to be able to decide upon an attack, have access to the best possible information about the objective. The decision should be based upon the information available to the commander at the time of deciding. 
Sweden, International Humanitarian Law in Armed Conflict, with reference to the Swedish Total Defence System, Swedish Ministry of Defence, January 1991, Section, pp. 70–71.