An accidental lasts the bar

It keeps working

An accidental lasts until the end of the bar. It counts for every later note on the same line or space. Here only the first B has a flat in front. The second B is still B flat.

The barline wipes it away

At the barline the accidental stops. In the next bar the note is back to normal. To cancel it sooner, inside the same bar, write a natural.

Remember

• An accidental lasts to the end of the bar.
• A barline stops it. A natural cancels it sooner.
• Before naming a note, look back along the bar.