Negative amplitude means the signal is attenuated relative to a reference point, so if you see e.g. -20dB, it means the signal is 1/10th of the reference value. dB on it's own is unitless, so you will see things like dBm (relative to 1mW â 0dB = 1mW), or dBV (relative to 1V â 0dB = 1V).
In Colorado, the offer is valid at the Denver Zoo and the Denver Art Museum. However, the Denver Art Museum is Sunday only, because they already offer free admission to everyone on the first Saturday of the month. This list does change, so check the Museums on Us website, before you go.
The Zoo borders Rock Creek Park with entrances at 3001 Connecticut Ave., on Harvard St. and on Beach Dr. It is open daily from 8:00 am to 8:00 pm between April 15th and October 15th. The rest of the year it is open daily from 8:00 am to 6:00 pm. It is closed on December /5th. Admission is free.