We are sorry that you are having these problems! Did you collect these measurements on a project or quick measurement? Currently, we cannot attach pictures to forum posts, but if you can insert the link to the measurements in question we can take a look and try to determine what the issue is.

Hi,you can find here the tests we did:

http://photosynq.org/projects/probando-probando/explore

Thanks Jesus,

It appears that the leaves that you were measuring were not covering the entire light guide (~1 cm square). This could be because the leaves were not properly placed in the clamp, or that the leaves were too small to cover the light guide. In either case, the chlorophyll fluorescence measurements (Phi2, PhiNPQ, PhiNO) would not be affected and should be accurate. However, absorbance measurements like relative chlorophyll content will not read properly without a masking (to reduce the measurement aperture) the light guide and recalibrating the instrument. Likewise, if the leaf is not covering the magnet, you will not get an accurate thickness reading.

Dear Dan, we were testing on the calibration sheets provided with the instrument, and with large chestnut leaves that were covering the whole of the rubber disc. That's why were were concern. We have used before other clips like the SPAD, Minolta, ASD's, and the Waltz PAM-2000, so the process to sample leaves is not unknown to us.

Could you check if there is any other possible failure?

Thanks for your help

Luis, I have found the problem. There is a problem with the SPAD and thickness calibration values. Please send an email to support@photosynq.org and include a link to this thread and we can get you sorted out.