## 1 Introduction  
Software development is a laborious process requiring knowledge of Programming Languages and various technologies. One of the major decisions we need to take is to choose the appropriate programming language. In recent decades, programming languages have advanced significantly. A lot of research in the field of programming languages is concerned with the design and implementation of a language, as we want to express programming ideas in a better and user-friendly way. Research in programming languages is an endless activity and the core of computing. We can expect new language features, concepts, paradigms, and programming mechanisms in the future. Despite advances in programming languages and platforms, most software is developed at a low level of abstraction relative to the concepts used by application programmers. This semantic gap is reduced by Domain-Specific Languages (DSLs) [1]. These languages cover the essential characteristics of the problem space in a way that they separate them from the details of the specific solution space [2]. These languages, when compared to general-purpose languages (GPLs), support a higher level of abstraction, and are closer to the problem domain than the implementation domain [3]. DSLs focus on domain abstractions, which empower end-users to program directly with concepts from the problem domain [4; 5]. The benefits of using DSLs are increased flexibility, productivity, reliability, and usability, which have been demonstrated in empirical studies [6; 7; 8]. Moreover, Domain-Specific Modeling Languages (DSMLs) [9; 10; 11; 12; 13] overlap in many ways with DSLs. These languages specify programs with models, and use visual blocks that raise the level of abstraction further [14; 15]. The abstract language syntax is usually defined by a metamodel that describes the language elements, the connections between them, and the structural rules that limit the model elements and their combinations [16; 17]. DSMLs are suitable for use in specific areas [18; 19; 20; 21; 22]. Dewesoft measurement systems [23], together with the Dewesoft X software package, are used to capture, process, and later analyze the measured data, using the domain-specific modeling language Sequencer [24; 25; 26] for the creation of measurement procedures. With the mentioned language, the end-users can create measurement procedures performed on the measuring system efficiently without professional computer knowledge. Further in this paper, we refer to DSML end-users as domain experts. The Sequencer language has been in use since 2010. More than 1000 domain experts use Dewesoft with the DSML Sequencer daily. Interacting with them shows customers' needs and desires for new possibilities of using our products [27]. As a consequence, the last improvement involved the development of a new language called RT-Sequencer. Our previous modeling language, Sequencer, was adapted to support, besides data acquisition (DAQ), another problem domain. RT-Sequencer now supports the creation of real-time (RT) procedures that run on Dewesoft controllers. Therefore, this paper presents the experience with DSML evolution and the implementation details behind the new language RT-Sequencer. The recent systematic mapping study [28] outlines that the DSL community focuses more on developing new techniques/methods rather than providing empirical evidence. Besides, almost no attention is given to the maintenance and evolution of DSLs in the literature, as argued in another study by [PERSON] and [PERSON] [29]. This paper tries to contribute to this field by presenting RT-Sequencer, a successor of the Sequencer [24; 27]. On the other hand, in another DSL literature review [30], authors report that most researchers experienced DSL's evolution, and that the evolution of a DSL affected the success of their DSL [30]. As shown in the findings from the same study [30], 40% of DSLs evolved due to the support of new domains, which was the case of Sequencer as well.