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If you're familiar with any other scoring software, Dorico's note input method is not a million miles away from Sibelius's method, or Finale's Simple Entry tool, with a few key differences. Basically, select the rest or other position where you want to start inputting, hit Return or Shift+N to show the caret (you can also double-click the place you want the caret to appear), then use the number keys along the top row of the keyboard to change duration (6 = quarter or crotchet, 5 = eighth or quaver, 7 = half or minim, and so on), and the letter keys A to G on the keyboard to input a pitch. To input a dotted note, hit the full stop or period key after you hit the number key for the duration and before you type A to G. For an accidental, use 0 for natural, - (minus, immediately to the right of 0) for flat, and = (equals, immediately to the right of minus) for sharp. Alternatively, if you have a MIDI keyboard, you can use a MIDI keyboard to specify pitch and accidental in one go.