Good advice from Foolestroupe about C/C#. The gap between these two notes is frequently narrowert than perfection demands, but don't dwell on it and it won't be a problem. It might occasionally be exposed in a chromatic run where you are required to play the two notes in sequence, such as might be encountered in some Northumbrian pipes tunes. In that case find ways to flatten the C natural a little, for instance by underblowing or covering all the holes except the top one and the one next to bottom - or both. Or go the Mary Bergin route, and get C natural by part-covering the top hole with all the others uncovered.

Ensuring accurate pitch across two octaves and into the third is a tall order, usually achieved only on high-end whistles. It invariably requires the inner bore to be perturbed by someone who knows what he's doing.

Just a thought on range, Leadfingers. You've forgottent he C# below the stave. The first person I saw and heard getting this note in fast play was the one-time all-Ireland champion Willis Patten. His disciples live on, and it's now second-nature for many a youngster in Northern Ireland. It's achieved by part-covering the end-hole with right-hand little finger. Obviously this note is not playable on low Ds, except possibly by MudGuard!