--- title: About the measurements description: Current Conditions --- [Skip to content](https://support.arable.com/about-the-measurements#main-content) - [English](https://support.arable.com/about-the-measurements) - [Español](https://support.arable.com/es/acerca-de-las-med) English Show submenu for translations [Submit a Support Ticket](https://support.arable.com/kb-tickets/new?hsLang=en) ![Arable_Logo_RGB_horizontal-2.png\]](https://support.arable.com/hs-fs/hubfs/Arable_Logo_RGB_horizontal-2.png?height=40&name=Arable_Logo_RGB_horizontal-2.png) Open main navigation Close main navigation - - [English](https://support.arable.com/about-the-measurements) - [Español](https://support.arable.com/es/acerca-de-las-med) English Show submenu for translations - [Submit a Support Ticket](https://support.arable.com/kb-tickets/new) - Go to Arable.com Go to Arable.com Welcome to the Arable Help Center - There are no suggestions because the search field is empty. 1. [Help Center](https://support.arable.com/?hsLang=en) 2. [Measurements](https://support.arable.com/measurements?hsLang=en) # About the measurements ## Current Conditions **Temperature** Ambient air temperature surrounding the device is measured using a carefully designed chamber that allows air to flow freely past the measurement sensor.  **Humidity** Relative Humidity is the ratio of water vapor in the air relative to the maximum possible. **Pressure** Barometric pressure is the pressure of the atmosphere exerted on an object below. The Mark measures barometric pressure at the same frequency as air temperature and relative humidity, so will accurately represent changes in barometric pressure caused by changing weather conditions. We present sea level corrected pressure using the following equation: Po=P\*exp(H\*g/(R\*T)). Our Arable Mark measures H, P, and T. R and g can be considered constants. **Sunlight** Sunlight is the amount of shortwave energy received from the sun and sky at a specific point. Sensors measure shortwave energy continuously over the course of a day, and Arable integrates these instantaneous values to obtain total daily sunlight for a given location.   #### Today’s Forecast **Temperature** Ambient air temperature surrounding the device is measured using a carefully designed chamber that allows air to flow freely past the measurement sensor.  Measurements are reported at 2m above ground. **Forecasted Precipitation** Forecasted Precipitation is taken from the state of the art weather forecast GEFS. It is a 115x115 km grid that is updated every 6 hours.  **Observed Precipitation** Observed Precipitation is the amount of precipitation that the Mark has measured thus far in a 24-hour period counting from 12am. The Mark measures observed precipitation using a microphone which records the frequency and intensity of raindrops as they hit the dome. #### Leaf Wetness (Condensation) **Last Wet** Time since the canopy was last wet. **Duration** Total amount of time the canopy has been wet over the past 24 hours. **10 Day Total Wet Hours** Total amount of time the canopy has been wet over the past 10 days. Rainfall is not included in the Leaf Wetness calculation. This measurement calculates condensation occurring when air temperature reaches the  dew point. #### Water Stress **Leaf Temperature** Leaf Temperature is measured by a sensor that is pointed down toward the plant canopy. The Mark calculates the leaf temperature using an infrared energy signal from the canopy and a temperature of the detector within the Mark. Higher leaf temperatures are correlated with water stress due to less evapotranspiration. Evapotranspiration (ET) serves to cool the leaves.  **Leaf Temperature - Air Temperature** Leaf Temperature minus Air Temperature is calculated using the difference between the surface temperature measured with the bottom infrared thermometer and the ambient air temperature.  Leaf to air temperature difference is based on the assumption that a canopy with available water transpires at its maximum potential resulting in a lower leaf temperature. When water becomes limiting, the leaf transpires less than maximum and the cooling effect of transpiration is reduced resulting in a higher leaf temperature. Positive values denote surface temperatures above air temperature. Higher positive differences indicate greater water stress. Negative values denote surface temperatures below air temperature. At mid-day, negative values indicate the surface is cooler than ambient air temperature. **Leaf to Air Temperature 4 Week Trend** Leaf to Air Temperature hourly trends for over the past 4 weeks. #### Plant Vigor **Chlorophyll Index** The Chlorophyll Index is a proxy for plant productivity and the chlorophyll and nitrogen content in the plant. The Mark’s spectrometer detects reflected light in the red edge and near infrared regions of the spectrum to calculate a Chlorophyll Index. A higher Chlorophyll Index is indicative of higher chlorophyll and nitrogen levels in the canopy and higher productivity in the plant. **Weekly % Change** Weekly % Change shows the percentage of change in the Chlorophyll Index from 7 days ago.  **Chlorophyll Index 4 Week Trend** Chlorophyll Index daily trends for over the past 4 weeks.   #### NDVI **NDVI** NDVI, or Normalized Differential Vegetation Index, represents the amount of green growing material present. The Mark’s spectrometer detects reflected light in the red and near infrared regions of the spectrum to calculate NDVI. A higher NDVI is indicative of more canopy cover. **Weekly % Change** Weekly % Change shows the percentage of change in NDVI  from 7 days ago.  **NDVI 4 Week Trend** NDVI daily trends for over the past 4 weeks.   #### Water In **Forecasted Precipitation** Forecasted Precipitation is taken from the state of the art weather forecast GEFS. It is a 115x115 km grid that is updated every 6 hours.  **Observed Precipitation** Observed Precipitation is the amount of precipitation that the Mark has measured thus far in a 24-hour period counting from 12am. The Mark measures observed precipitation using a microphone which records the frequency and intensity of raindrops as they hit the dome. #### Water Out **Forecasted Evapotranspiration** Forecasted Evapotranspiration for 10 day window. Forecasted ET for a specific location is from the GFS weather forecast that is updated every 6 hours. **Observed Evapotranspiration** Observed Crop Evapotranspiration for each day in a 10 day window. Crop Evapotranspiration is the quantity of water lost through evaporation and transpiration above the plant canopy. This calculation relies on multiple inputs from the device including four component net radiation and site-specific microclimate characteristics, all of which are measured directly by the Mark.  A value of 0 is indicative of a wet environment (usually following a storm) whereas a value of 10 indicates an environment that is rapidly transporting water into the atmosphere. - [Getting Started](https://support.arable.com/getting-started?hsLang=en#main-content) - [User Guides](https://support.arable.com/getting-started?hsLang=en#user-guides) - [Installation, Setup, and Troubleshooting](https://support.arable.com/getting-started?hsLang=en#installation-setup-and-troubleshooting) - [Frequently Asked Questions](https://support.arable.com/frequently-asked-questions?hsLang=en#main-content) - [Device Health](https://support.arable.com/frequently-asked-questions?hsLang=en#device-health) - [Guides](https://support.arable.com/guides?hsLang=en#main-content) - [Mark 3 and Accessories](https://support.arable.com/guides?hsLang=en#mark-3-and-accessories) - [Arable Developer API](https://support.arable.com/arable-developer-api?hsLang=en) - [Maintenance, cleaning and storage](https://support.arable.com/maintenance-cleaning-and-storage?hsLang=en) - [Measurements](https://support.arable.com/measurements?hsLang=en#main-content) - [Rainfall](https://support.arable.com/measurements?hsLang=en#rainfall) [![Chill listening crop-3](https://support.arable.com/hs-fs/hubfs/Logos/Arable_Logo_RGB_horizontal.png?width=100&height=24&name=Arable_Logo_RGB_horizontal.png "Chill listening crop-3")](https://arable.com) Arable Help Center Copyright © 2026, Arable