Study Procedure

The first page of the app allows the experimenters to select the trial they want to perform and to input their name (Multimedia Appendix 2, Screenshot 1). For all of the trials except the ambient lighting trial, the experimenter is required to enter the illuminance measurement at which the trial is being performed.

To complete a single trial, an experimenter scanned each barcode in the series once. Each trial was performed 10 times on each of the 4 devices, by 2 independent experimenters. The experimenters went through a training period where they each performed each trial twice to familiarize themselves with the scanning procedure. For all trials except the curvature trial, the paper containing the barcode was fastened to a flat surface. For the curvature trial, the vials to which the barcodes were adhered were fastened to the surface with the barcodes facing up.

When the experimenter begins a trial, a screen is shown that indicates how many scans are remaining in the trial and which barcode must be scanned next (Multimedia Appendix 2, Screenshot 2). When the user taps the scan button, the device must be in the user’s hand, which must be resting on the table surface 8 inches to the right of the sample. Only after the scan button has been pressed may the user move the device to attempt to scan the barcode. This was done to eliminate disparities between scans due to the experimenter maintaining the exact position and height of the device, which promotes subsequent scans being far quicker than the initial scan.