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: In contrast , eucalcemic patients exhibited no change in mean calcium values over the same time period ( 2 . 3 + / - 0 . 05 to 2 . 3 + / - 0 . 05 mmol / L [ 9 . 2 + / - 0 . 2 to 9 . 2 + / - 0 . 2 mg / dL ] ) .
### Output Text:
In contrast , eucalcemic patients exhibited no change in mean <span class="chemical">calcium</span> values over the same time period ( 2 . 3 + / - 0 . 05 to 2 . 3 + / - 0 . 05 mmol / L [ 9 . 2 + / - 0 . 2 to 9 . 2 + / - 0 . 2 mg / dL ] ) . 