One of the best chromatic tuner pedals! Boss says:

Features

• Gold standard pedal tuner enhanced with Waza craftsmanship
• Refined buffer circuitry for exceptionally pure signal pass-through
• Buffer can be turned off for true-bypass operation
• Sharp 21-segment LED meter with brightness control
• High Brightness mode enhances meter visibility when playing outdoors
• Accurate to +/- one cent
• Accu-Pitch Sign function provides visual verification when tuning is complete
• Chromatic mode for tuning to any pitch
• Guitar and Bass modes for tuning by string number, with support for 7-string guitars and 5- and 6-string basses
• Flat tuning options support down tuning up to six semitones below standard pitch (Guitar mode) and three semitones below (Bass mode)
• The output automatically mutes when the tuner is engaged, allowing for silent tuning on stage
• Bypass output jack for use as an unmuted output and signal splitter
• DC output jack for distributing power to other pedals (requires optional PSA-series adaptor and PCS-20A parallel cable)
• Made in Japan
• BOSS five-year warranty