## 1 Introduction  
Smartphones have played an essential role as communication devices [1]. People perceive a smartphone as a necessity in everyday life and for work because of its various functionalities, including Internet service [2]. The penetration rate of smartphones has exceeded 50% in many western countries, and more than 80% of mobile phone users use smartphones in South Korea [3]. Because smartphone penetration is increasing and the market is becoming saturated, companies are making great efforts to satisfy not only technological progress but also user's perceived emotion [4]. In order to gain a competitive edge over competitors in a highly competitive market, research has been actively undertaken to determine the relationship between various dimensions related to the design of smartphones, such as length, width, thickness, and weight, and the user's subjective feelings. [PERSON] et al. [5] studied the relationships between subjective fatigue ratings and the physical features of smartphones, including size, weight, shape, and material. [PERSON] et al. [6] identified optimal reach zones for the back-side interaction on smartphones with different widths and lengths based on subjective discomfort and muscle activation data when various tasks were given. [PERSON] et al. [7] investigated the touch performance of one-handed thumb interactions with iPhone 5S, 6, and 6 Plus by measuring the tapping time, hit count, and thumb-tip and determined reachability issues for large smartphones. In addition, [PERSON] and [PERSON] [8] determined the preferred size of smartphones with hand anthropometry data and in terms of smartphone handiness. With the increase of information provided by smartphones and the development of technologies related to flexible displays, smartphones including curved displays are being launched. This type of display is called \"edge\", which means a curved display implemented on one or both sides [9]. In fact, the Galaxy Note Edge was launched as the first smartphone with an edge screen in 2014. Since then, the Galaxy Edge series has steadily been released. Moreover, other major manufacturers also started to launch smartphones with edge screens, such as the Xiaomi Note 2 and Vivo Xplay 6. From the viewpoint that design variables such as size, shape, etc. are important characteristics that affect subjective satisfaction for users, the curvature of the side display can give a different feeling to the user compared to the flat display [10]. However, this issue has not been dealt with in previous studies. A few studies investigated the various facets of smartphones with curved screens. [PERSON] et al. [11] investigated the effect of the curvature of the screen and hand size of the user on the physical comfort of using curved smartphones. [PERSON] et al. [12], however, endeavored to determine the optimal curvature of the screen and thickness of the smartphone in terms of physical comfort using the muscular activities of the hand. However, they only focused on the curvature of the main screen. [PERSON] et al. [13] studied the effect of display curvature and hand length on the usability of smartphones. The results showed that the perceived grip comfort in two situations, calling and texting, was the highest when the hand length was medium. In addition, the value of the perceived grip comfort of the curved display was lower than that of the flat display for all hand lengths. However, this study did not compare perceived grip comfort between curvature displays. Therefore, it is necessary to study the grip comfort according to the specifications of the curvature display on the smartphone side. Grip/usage pattern and personal information such as gender, age, and size of hand should be considered to determine the effect of the physical dimension of mobile phones on user satisfaction. Previous studies related to convenience for handheld devices were performed mainly on the assumption that only a single hand is used [14].