## 1 Introduction
To estimate potential damage on in-line equipment, [PERSON] and [PERSON] [7] correlated the impact accelerations from the IS 100 with the frequency and severity of damage. This study also determined the effects of tuber mass and temperature on the damaged surface. [PERSON] et al. [4] developed two models that combined sensor index values with dry matter content and tuber temperature to predict discoloration. These models showed moderate coefficients of determination. In a study by [PERSON] et al. [1], peak acceleration and integral average acceleration recorded by an electronic device were used to assess potato damage resulting from dynamic impacts during combined harvesting in various conditions. The study allowed for the influence of variety, soil type and combine harvester operating speeds on tuber damage during harvesting to be determined. The impact recorders have been widely used in studies conducted by [PERSON] and [PERSON] [10], [PERSON] and [PERSON] [23], and [PERSON] and [PERSON] [24] to determine damage thresholds (bruising). It should be noted that other factors with respect to the physical and biological properties of tubers may affect bruising thresholds [25; 26], including, as follows: the variety [27]; tuber hydration [28]; and tuber flesh temperature [12; 29]. Electronic recorders mimic the potential of impact damage to a single tuber as it moves through harvesting and post-harvest processing machines; however, they do not measure tuber characteristics. Therefore, the penetration of the tubers into the material they impact, and the resulting peak acceleration, will be smaller compared to impacts caused by electronic recorders. This can cause difficulties in determining the exact relationships between the recorded parameters and tuber damage, as was confirmed in tests conducted by [PERSON] et al. (2010) and [PERSON] et al. (2013). In one study ([PERSON] et al., 2016), it was shown that electronic recorders with synthetic housings produced higher peak force values than real potatoes with an implanted acceleration measuring unit. Despite many studies, the relationship between the parameters registered by recorders and the degree of damage is still poorly understood. Predicting the probability of bruising on tubers based on measurements from these devices is based on the determining the relationship between impact acceleration and product damage. Changes in velocity, as the second recorded parameter (change in velocity), also occur during impacts with varied initial velocities. Typically, this parameter has been used to characterize the impact surface. Despite the wide use of recorders in various potato tuber studies, no direct relationship exists between the acceleration and velocity changes recorded by impact recorders and the damage rate. This study aimed to determine the effect of the initial impact velocity and the type of impact surface on the potential damage to potato tubers during free-fall tests, and to answer the question of how the impact parameters, peak acceleration and the change in velocity during the impact, recorded with a device imitating a potato tuber with a piezoelectric sensor, can be related to the tuber damage index.