Tecnai on-line help manual -- Options - UT Southwestern

<strong>Tecnai</strong> on-line help Options 68Options Software version 2reference points is opened, the software will ask to redo the reference points immediately. If thereference points are not redone at this stage, the software will display the stored locations and tracks intheir original configuration. The reference points can then still be done later.Setting reference points for new dataDuring the procedure wherein new reference points are defined, the operator is askedto drive the stage to 2 or 3 points that can be recognized. It is suggested to avoidpoints that lie on the opposite side of the center as this will make it much more difficultto decide later whether the specimen has been reloaded in the same way or upsidedown. If at least two points are defined lying at an angle of about 120°, then it will beeasier to decide. Three points make recognition of an upside-down position of thespecimen even easier. If no third reference point is to be set, then simply press OKwhile keeping the specimen stage at the same location as for point 2. The third point will then beignored.Redoing reference points for old dataIf a file containing reference points is reopened, the software will suggest to gothrough the procedure for relocating the old reference points. The software will showthe distribution of the old reference points and list the label of each point in turn. Thereference point locations will be updated with the new ones, once a reference pointhas been found again.During this procedure this software can assist in finding back the old reference points through the Assistfunction. The Assist function will list a number of possibilities depending on which reference points mustbe found again:• Move the specimen stage to the old location for point 1.• Move the specimen stage in a circle, around 0,0 for point 1, around 1 for point 2, etc.• Calculate alternative locations for points 2 and 3 on the assumption that the specimen is upsidedown.After finding reference point 1, the software will calculate what the most likely new location is forreference point 2 and ask if the stage must be driven there. The same is done for point 3 (if a thirdreference point had been set originally).For each reference point found back as well as the whole set of the reference points the software will gothrough a number of consistency checks (distances between old points and new points comparable,angles from the center of gravity of the old three-point triangle and old points and the center of gravity ofthe new three-point triangle and new points comparable).The software can handle rotation, shift and mounting upside down of the specimen. The software alsocalculates a 'stretch' parameter that is related to the percentage difference in dimensions between oldand new reference points. The software cannot however accommodate severe distortions due tobending of the specimen, so some care should be taken to ensure the integrity of the specimen. Thevarious values can be displayed under Show ref. pt. data.