Ensure the OMA tube is still sitting on a flat surface, in the shade or your shadow and with the sample filled to the level line.
Place the cap on the tube, select ‘camera’ on your smart device and again check that it is in portrait mode. Place the lens of the camera over the hole as you did for the baseline photo and position the image on your device so that it is in the centre of the aperture hole.
NOTE: If you cannot see the Secchi disk in the image on your device, you still need to take the photo to allow the device to compare minute variations in the image. The OMA app will display a focus indicator.
Take the photo and accept the image.