some of which are explored and explained below. Not all methods can be used for all organisms, due to size or other properties. For example, a diatom does not have the same properties as a plant, which would place limitations on methods that could be used to infer turgor pressure. Units Units used to measure turgor pressure are independent from the measures used to infer its values. Common units include bars, MPa, or newtons per square meter. 1 bar is equal to 0.1 MPa. Methods Water potential equation Turgor pressure can be deduced when the total water potential, Ψw, and the osmotic potential, Ψs, are known in a water potential equation. These equations are used to measure the total water potential of a plant by using variables such as matric potential, osmotic potential, pressure potential, gravitational effects and turgor pressure. After taking the difference between Ψs and Ψw, the value for turgor pressure is obtained. When using this method, gravity and matric potential are considered to be negligible, since their values are generally either negative or close to zero. Pressure-bomb technique The pressure bomb technique was developed by Scholander et al., reviewed by Tyree and Hammel in their 1972 publication, in order to test water movement through plants. The instrument is used to measure turgor pressure by placing a leaf (with stem attached) into a closed chamber where pressurized gas is added in increments. Measurements are taken when xylem sap appears out of the cut surface and at the point which it doesn't accumulate or retreat back into the cut surface. Atomic force microscope Atomic force microscopes use a type of scanning probe microscopy (SPM). Small probes are introduced to the area of interest, and a spring within the probe measures values via displacement. This method can be used to measure turgor pressure of organisms. When using this method, supplemental information such as continuum mechanic equations, single force depth curves and cell geometries can be used to quantify turgor pressures within a given area (usually a cell). Pressure probe This machine was originally used to measure individual algal cells, but can now be used on larger-celled specimens. It is usually used on higher plant tissues but was not used to measure turgor pressure until Hüsken and Zimmerman improved the method. Pressure probes measure turgor pressure via displacement. A glass micro-capillary tube is inserted into the cell and whatever the cell