A system comprising an anesthetic vaporizer, and a first sensor, in communication with an inlet conduit, the inlet conduit configured upstream from the anesthetic vaporizer and to deliver a flow of carrier gas to the anesthetic vaporizer, wherein the first sensor produces a first sensor signal indicative of a composition of the carrier gas in the inlet conduit; a second sensor, in communication with an outlet conduit, the outlet conduit configured downstream from the anesthetic vaporizer and to deliver a flow of combined carrier gas and anesthetic from the anesthetic vaporizer, wherein the second sensor produces a second sensor signal indicative of a composition of the combined carrier gas and anesthetic added by the vaporizer; a third sensor, in communication with the inlet conduit and configured downstream or upstream relative to the first sensor, wherein the third sensor produces a third sensor signal indicative of the composition of the carrier gas in the inlet conduit; a fourth sensor, in communication with the outlet conduit and configured downstream or upstream relative to the second sensor, wherein the fourth sensor produces a fourth sensor signal indicative of the composition of the combined carrier gas and anesthetic added by the vaporizer; and a controller that receives the first, second, third and fourth sensor signals (22, 24, 26, 28), computes a first anesthetic output with the first sensor signal and the second sensor signal, and further computes a second anesthetic output with the third sensor signal and the fourth sensor signal, wherein the first, second, third and fourth sensors (1, 2, 3, 4) are ultrasonic time-of-flight sensors, the first and third sensor signals (22, 24) are indicative of acoustic time-of-flight across the inlet conduit, and the second and fourth sensor signals (26, 28) are indicative of acoustic time-of-flight across the outlet conduit; wherein the first sensor is mounted to a conduit (20, 80) without inclination to the direction of flow to transmit an acoustic wave perpendicular to the flow and mounted across from a respective alternatively flat and sloped surface which is configured to split the acoustic wave from the first sensor so that a portion of the acoustic wave is transmitted back to the first sensor and another portion of the acoustic wave is transmitted to the third sensor; wherein the third sensor is mounted to the conduit (20, 80) without inclination to the direction of flow to transmit an acoustic wave perpendicular to the flow and mounted across from a respective alternatively flat and sloped surface which is configured to split the acoustic wave from the third sensor so that a portion of the acoustic wave is transmitted back to the third sensor and another portion of the acoustic wave is transmitted to the first sensor; wherein the second sensor is mounted to a conduit (30, 80) without inclination to the direction of flow to transmit an acoustic wave perpendicular to the flow and mounted across from a respective alternatively flat and sloped surface which is configured to split the acoustic wave from the second sensor so that a portion of the acoustic wave is transmitted back to the second sensor and another portion of the acoustic wave is transmitted to the fourth sensor; and wherein the fourth sensor is mounted to the conduit (30, 80) without inclination to the direction of flow to transmit an acoustic wave perpendicular to the flow and mounted across from a respective alternatively flat and sloped surface which is configured to split the acoustic wave from the fourth sensor so that a portion of the acoustic wave is transmitted back to the fourth sensor and another portion of the acoustic wave is transmitted to the second sensor.