A distance or angle can be easy to read once—and surprisingly easy to lose track of while you continue editing a molecular structure. If you are comparing a geometry before and after a move, or trying to keep an annotation visible while inspecting a model, the key is knowing when a measurement is temporary and when it has been saved as a label.
SAMSON’s Measure editor can show bond lengths, distances, angles, and torsions. Open it from the left-side menu in the viewport, or use Ctrl/Cmd + M. Then click the relevant atoms in sequence:
- Click a bond to show its length.
- Click two atoms to show the distance between them.
- Click three atoms to show the angle.
- Click four atoms to show the torsion.
This gives you a quick readout without first creating a permanent annotation. But there is an important limitation: an unsaved measurement is temporary. It stays visible regardless of zoom, but the next measurement replaces it. So if you need to keep a result while making another measurement, press Enter to save it as a label in the document.
A practical measure-and-edit loop
- Measure the feature you want to monitor. Choose the bond or atoms in the order needed for the measurement.
- Save measurements you need to compare or revisit. Press Enter so the result becomes a document label rather than a temporary readout.
- Continue editing the structure. Saved measurements update automatically when their associated atoms move or their charges change. This can help you follow a geometric value while using Move editors or interactive minimization.
- Keep the document if the annotations matter later. Measurement labels are saved when the document is saved in a SAMSON format,
.samor.samx.
The distinction matters during model exploration: a temporary measurement is useful for a quick check, while a saved label is the better choice for an annotation you want to preserve alongside other measurements.
Saved distance labels can also provide more than the displayed atom-to-atom value. Select the label and open the Inspector to see the atoms associated with it. For an atom-atom distance, the Inspector also shows additional measurements for projections on planes.
Make annotations readable
Saved measurements behave like other labels: their visibility depends on zoom, and their font, color, and offset can be adjusted. The Inspector also lets you change the colors of distance lines and angle planes. If an appearance change makes a label harder to read, you can reset line or angle colors by double-clicking the associated text in the Inspector. To reset the text color, use the clear button beside Text color.
For consistency across a set of annotations, the Inspector lets you set a font for an individual label. Preferences > Rendering > Labels provides a font for labels without an individually specified font, as well as the number of decimal places used for angles and distances created with the Measure editor. Adjusting these settings can make a collection of measurements easier to scan without changing the underlying structure.
One useful habit is to save only the measurements you expect to use again, then inspect their labels after moving the structure. That keeps quick checks quick while preserving the values that help you understand or communicate a model.
For the full instructions, see the SAMSON Measuring documentation.
Note: SAMSON and all SAMSON Extensions are free for non-commercial use. Get SAMSON.