Chlorophyll meter readings were taken on an industrial potato crop R12 used for frying and crisp production.
The crop suffered low rainfall post transplant and was slow to establish. OMEX Bio 8 and Zincprod were applied as foliar sprays to promote root and shoot growth.
The crop shown in the photos is approximately 65 days post transplant and uneven in growth due to abiotic stress in dry conditions.
Control: 58.0 = SPAD 47.3 = 0.0486 mg/cm2
Bio 8: 61.0 = SPAD 50.3 = 0.0532 mg/cm2
Zincprod: 62.6 = SPAD 51.9 = 0.0558 mg/cm2
Higher levels of photosynthesis will lead to increased sugar production and improvements in crop development in terms of shoot and root growth, earlier flowering and improved translocation of sugars from source to sink for bigger, heavier tuber counts and higher percentages of dry matter (starch) in the tubers. 
Conversion from atLEAF meter readings to equivalent SPAD and mg/cm2 chlorophyll – https://www.atleaf.com/SPAD