Conversely, in 2002, a few local authorities, apparently under pressure from distributors and cinema chains, ignored the BBFC's ruling that Spider-Man receive a 12 rating, and allowed children younger than 12 to see the film. However, the BBFC were already in the process of replacing the 12 rating with a new 12A, which allowed under-12s to see the film if accompanied by an adult, so shortly afterwards, Spider-Man was reclassified as 12A. The first 12A certificate awarded was for The Bourne Identity . 
• where the material is in breach of the criminal law, or has been created through the commission of a criminal offence
• where material or treatment appears to us to risk harm to individuals or, through their behaviour, to society. For example, the detailed portrayal of violent or dangerous acts, or of illegal drug use, which may cause harm to public health or morals. This may include portrayals of sadistic or sexual violence which make this violence look appealing; reinforce the suggestion that victims enjoy sexual violence; or which invite viewer complicity in sexual violence or other harmful violent activities
• where there are more explicit images of sexual activity in the context of a sex work (see below) or where the primary purpose of the images in question is sexual arousal In the case of video works, which may be more accessible to younger viewers, intervention may be more frequent than for cinema films.
Film speed is found from a plot of optical density vs. log of exposure for the film, known as the D –log H curve or Hurter–Driffield curve. There typically are five regions in the curve: the base + fog, the toe, the linear region, the shoulder, and the overexposed region. For black-and-white negative film , the "speed point" m is the point on the curve where density exceeds the base + fog density by when the negative is developed so that a point n where the log of exposure is units greater than the exposure at point m has a density greater than the density at point m. The exposure H m , in lux-s , is that for point m when the specified contrast condition is satisfied. The ISO arithmetic speed is determined from: