You have several options:
In the "Calculate distance" tab:
Option 1: Click any odorant on the map, and it will be assigned as "Odorant 1". Click a second odorant, and it will be assigned as "Odorant 2". Their distance will appear in the gray windo at the upper right hand side.
Option 2: Select an "Odorant 1" from the pull-down menue (use either CAS, CID or smell). Select an "Odorant 2" from the pull-down menue (use either CAS, CID or smell). They will appear color-coded in the map, and their distance will appear in the gray windo at the upper right hand side.
In the "Choose multiple points" tab:
Option 1: Click sequentially on as many points as you would like to include in your group.
Option 2: Sequentially select an "Odorant 1" from the pull-down menue (use either CAS, CID or smell). Each odorant selected will be added to the group.
Option 3: You can choose a pre-selected group from the pull-down menue.
In all cases, once you have selected your set, you can both download all the pairwise distances by downloading the data file, and download a figure of your selected odorants in OdorSpace by downloading the figure file.
Note that you can click the left button and mark an area to zoom.
The coordinates of points displayed are the first and second components in a principal components analysis of the collection of odorants. The distances which are calculated are the euclidean distances based on 32 selected physicochemical properties as explained in Haddad et. al. (2008)
The calculated distance between odorants corresponds to the difference in level of neural activation measured in 7 different studies, mostly in rodents. See the article for details.