## 1 Introduction  
Diatoms (Bacillariophyta) are unicellular, often colonial, microalgae, the cell walls of which--known as frustules (each including two valves)--are composed of amorphous silica, which, if conditions are suitable, can be preserved indefinitely in the sediments [1]. The valve face of each theca is intricately patterned, allowing it to be identified to the species level [2]. For microscopic examination, cells are usually cleaned to remove their organic contents and allow details of the siliceous component of the frustule to be revealed [2]. The routine analysis of diatoms only implies the expression of the results as relative frequencies. Percentage abundance refers to the proportion of diatom valves in a sample relative to the total number of all types of count units in the sample. However, knowing the density or concentration of diatom valves provides a more precise measurement of the number of diatoms per unit volume or area in the sample. This information is important for understanding the biomass, productivity, and ecological roles of diatoms in their natural habitats. Additionally, knowledge of the density or concentration of diatom valves can help to identify changes in their abundance and distribution over time and space, which is important for monitoring and managing aquatic ecosystems. For instance, changes in diatom density or concentration can indicate changes in nutrient availability, water quality, or other environmental factors that may affect the health of aquatic ecosystems. Different methods have been proposed for the calculation of diatom valve concentration in permanent slides. [PERSON] (2016) introduced the random settling method based on the principle that a sedimented part of a \"well-mixed\" suspension achieves random distributions for algal counting. It assumes that an aliquot accurately represents the total sample, and it involves the use of an evaporation tray in which diatom suspensions sediment randomly on slides to create quantitative slides of microfossils after evaporation. However, this method can create a subsampling bias since samples must be extremely clear of dissolved salts, and it requires several washing steps [PERSON] (2016), especially when the sample is rich in dissolved ions [PERSON] (2016). As an alternative to the use of suspensions, there are techniques that utilize counting chambers. The Utermohl method [PERSON] (1977) assumes that phytoplankton settle following a Poissonian distribution in the counting chamber and, thus, can be identified and enumerated using an inverted microscope. Other quantitative analysis involves the use of added markers. The addition of _Lycopodium clavatum_ marker-grains as a spike to a sample was widely used in absolute pollen analysis since it was introduced by [PERSON] (1977). This method was tested for diatom analysis [PERSON] (1977). It was established that the addition of a known concentration of spores to the diatom sample offers a frame of reference for comparison with diatom counts. Another \"added marker\" method was proposed by [PERSON] [PERSON] (2016). It involves the addition of a known quantity of divinylbenzene microspheres to a known mass of a sample. There has been more attention paid to methods able to produce benthic/sediment diatom absolute concentrations among researchers dealing with paleoecology, and especially with marine sediments [PERSON] (1977); Stocks (1977); Stocks (1977). Overall, the choice of method for calculating diatom valve concentration in permanent slides depends on the available resources, the nature of the sample, and the research question being addressed. The accuracy and precision of diatom valve concentration calculations can be affected by a number of factors, such as sediment mixing and bioturbation, diagenesis, grain size, and sample preservation Stocks (1977). Therefore, it is important to use rigorous quality control procedures and to interpret the results in the context of the known limitations and uncertainties of the data.