Related Rule
Practice Relating to Rule 18. Assessment of the Effects of Attacks
The Military Manual (1993) of the Netherlands states: “During the selection of targets and the preparation of attacks, an attack must be renounced if it can be expected that it may cause damage which is excessive in relation to the anticipated military advantage.” 
Netherlands, Toepassing Humanitair Oorlogsrecht, Voorschift No. 27-412/1, Koninklijke Landmacht, Ministerie van Defensie, 1993, p. V-11.
The Military Manual (2005) of the Netherlands states:
0542. When selecting objectives and preparing to attack, the attacker must:
- refrain from an attack which may be expected to result in collateral damage on a scale which would be excessive in relation to the expected military advantage.
0543. When not to attack
An attack should not proceed when an obvious lack of proportion appears to exist between expected military advantage and expected collateral damage. The decisive factor is whether a normally alert attacker, in receipt of and acting on due information, could have expected the excessive damage among the civilian population and civilian objects.
0546. When attacking mixed objects … it must be carefully considered whether the military advantage expected from eliminating the military element of the mixed objective outweighs the damage done to the civilian population, by damaging or destroying the civilian element of the mixed object or ending its civilian function. In any case, the disabling or destruction of the military element must yield a clear military advantage (cf. AP I [1977 Additional Protocol I] Article 52). In addition, the civilian population must not be excessively affected (cf. AP I Article 51). 
Netherlands, Humanitair Oorlogsrecht: Handleiding, Voorschift No. 27-412, Koninklijke Landmacht, Militair Juridische Dienst, 2005, §§ 0542, 0543 and 0546.
According to the Government of the Netherlands, commanders have to take all the precautionary measures required by Article 57 of the 1977 Additional Protocol I when carrying out an attack. 
Netherlands, Lower House of Parliament, Memorandum in response to the report on the ratification of the Additional Protocols, 1985–1986 Session, Doc. 18 277 (R 1247), No. 6, 16 December 1985, p. 7, § 17.