In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Pain rating was performed using a computerized visual analogue scale ( 0 - 100 ) digitized at 1 / s , either immediately online or one hour or one day after injection .
### Output Text:
Pain rating was performed using a computerized visual analogue scale ( 0 - 100 ) digitized at 1 / s , either immediately online or one hour or one day after injection . 