In this study, the concentration of hemoglobin within the subject's blood will be reduced in a controlled manner by administering fluids intravenously. The accuracy of a noninvasive hemoglobin sensor(s) will be assessed by comparison to hemoglobin measurements from a laboratory analyzer.

Study Site 1:

Inclusion Criteria:

• Has physical status between ASA 1 or 2
• Able to communicate in English

Exclusion Criteria:

• Pregnant or sexually active without birth control.
• Hemoglobin less than 11g/dL
• Known alcohol or drug abuse
• Skin abnormalities affecting the digits such as psoriasis, eczema, angioma, scar tissue, burn, fungal infection
• Nail polish
• Head injury with loss of consciousness within the last year
• Known neurological and psychiatric conditions.
• Known concurrent chronic usage of psychoactive or anti-convulsive drugs within the last 90 days, or use in the last 7 days (i.e. tricyclic antidepressants, MAO inhibitors, lithium, neuroleptics, anxiolytics or antipsychotics. Except SSRIs
• Subject has any medical condition which, in the judgement of the investigator, renders them inappropriate for participation in this study, such as Raynaud's syndrome
• Hypertension: Systolic BP >= 140 mmHg or Diastolic BP >= 90 mmHg
• Baseline heart rate <50 beats per minute

Study Site 2:

Inclusion Criteria:

• Male or female
• 18-35 years of age
• Physical status of ASA I or II
• Able to read and communicate in English
• Has signed written informed consent
• If female, non pregnant. If female subject is currently sexually active and not on birth control they must have a negative pregnancy test prior to study enrollment.

Exclusion Criteria

• Age less than 18 yrs and greater than 35 years
• Hemoglobin less than 12 g/dL
• ASA physical status of III, IV, or V
• Pregnant or sexually active without birth control
• Subject has known drug or alcohol abuse
• Subject has skin abnormalities affecting the digits such as psoriasis, eczema, angioma, scar tissue, burn, fungal infection, substantial skin breakdown, nail polish or acrylic nails.
• Subject has experienced a head injury with loss of consciousness within the last year
• Subject has known neurological and psychiatric disorder that interferes with the subjects level of consciousness
• Known or concurrent chronic usage of psychoactive or anticonvulsive drugs within the last 90 days, or any use in the last 7 day (i.e. tricyclic antidepressants, MAO inhibitors, lithium, neuroleptics, anxiolytics or antipsychotics, except SSRIs).
• Subject has any medical condition which in the judgment of the investigator, renders them inappropriate for participation in this study, such as Raynauds Syndrome.
• Hypertension: Systolic BP >140 mmHg or Diastolic BP > 90 mmHg.
• Baseline heart rate < 50 bpm.
• Inability to tolerate sitting still or minimal movement for up to 90 minutes