Do this:
1) Apply a force to the tuning pin so that it moves and produces the pitch you need.
2) When you reach the target pitch, do NOT reduce the force on the hammer. Keep it there. Confirm with your ear that this pitch is what you want. (This is meant to be done using DSU which you can easily judge as correct by the sound of the unison.)
3) Slowly remove the hammer force, listening to the sound of the DSU.
Did the sound change? If it did, then the unbending and untwisting were too much for the hammer technique you were using.
This illustrates the powerful feedback one can get by using the first two phases of hammer technique.
Phase 1 - Apply force to hammer to produce target pitch. Do not remove or reduce force when target pitch is reached.
Phase 2 - Remove the hammer force, listening carefully to the sound of the DSU. If the DSU colour changes, then the unbending/untwisting was too much.
This is usually done as part of the massage down of the move and massage technique. When the massage down is too much, the unbending that occurs in Phase 2 will be enough to raise pitch.
To fix this, move the pin foot so that the pitch is not as sharp of the target pitch. Now you won't have to massage (bend) the pin down as much to reach the target pitch and there will be less unbending.
Phase 3, which also gives good feedback on the appropriateness of your chosen hammer technique, is done after the hammer force is removed. It is not always done. When it is done, it is done to check stability.
Phase 3 is when the tuner uses the Bend Test or a Test Blow. If the pitch changes, which can easily be heard using DSU, then the hammer technique needs to be changed so that the NSL tension is left tighter or looser, depending on the result of the Test Blow or Bend Test.
This video explains it a bit more.
