a positioning drive 10 moves a part 11 which can be shifted at least between a position 1 and a position 2 . a displacement sensor 19 generates displacement signals 20 which , like position signals 17 generated by a position detector 16 , are delivered to a displacement determination device 18 . displacement determination device 18 exchanges signals with a control arrangement 12 . displacement determination device 18 makes available to a data set selector 14 signals with which data set selector 14 selects one data set 15 from various data sets stored in a memory 13 , and delivers it to control arrangement 12 . after receiving the &# 34 ; start reference run &# 34 ; signal 21 , control arrangement 12 starts a reference run . fig2 describes one possibility for carrying out the reference run . starting from action 0 , the idle position , action 1 is initiated after actuation of the &# 34 ; start reference run &# 34 ; signal 21 . position 1 is thereby reached . once position 1 has been reached , the counter for displacement determination device 18 is started ( action 2 ), and the instruction is given to reach position 2 ( action 3 ). once position 2 has been reached , in action 4 the counter for displacement determination device 18 is stopped . then , in action 5 , a data set selection 14 is performed for positioning drive 10 . after data set selection 14 , the end of the reference run has been reached . the arrangements shown in fig1 and 2 operate as follows : the apparatus is in the idle position ( action 0 ); part 11 may be in any position . memory 13 contains a variety of data sets , none of which have yet been reported to control arrangement 12 as being relevant . the reference run is initiated via the &# 34 ; start reference run &# 34 ; signal 21 . the signal could , for example , be generated during the first actuation of positioning drive 10 . during action 1 , control arrangement 12 must send control signals to positioning drive 10 in order to reach position 1 . it is conceivable in this context for positioning drive 10 to move part 11 at a predefined rotation speed in a predefined direction . for example , assume that positioning drive 10 will first move part 11 to the right as shown in fig1 . if the initial position of part 11 is to the right of position 1 , part 11 will first reach position 2 . position detector 16 thereupon delivers position signals 17 to displacement determination device 18 and to control arrangement 12 , informing control arrangement 12 that position 2 has been reached . position signals 17 can be generated , for example , via switches or microswitches whose output signal changes as soon as part 11 reaches the position equipped with the switch . it is also conceivable , if an electric motor is present in positioning drive 10 , to utilize the armature current profile or the change over time in the armature current for position analysis . if , for example , a position is embodied as a mechanical end stop , the armature current will then rise as a result of the jamming situation . if specific limits are thereby exceeded , position detector 16 delivers position signals 17 which indicate that the mechanical end stop has been reached . the end stop can also be detected via a rotation speed analyzer if the rotation speed of positioning drive 10 has assumed a value of zero for a specific time interval . also conceivable is a combination of the position determination possibilities just described , for example an analysis of switch signals together with detection of mechanical end stops . in action 1 , part 11 has arrived at position 2 . control arrangement 12 thereupon authorizes a reversal in the rotation direction of positioning drive 10 . part 11 now moves to the left and ultimately reaches position 1 , which position signals 17 report to displacement determination device 18 and control arrangement 12 . if part 11 is located to the left of position 1 in the initial position , position 1 is reached without a reversal in rotation direction , with the predefined movement to the right . the condition necessary for actions 2 and 3 is thus met . in the context of action 2 , the counter for displacement determination device 18 is started . for example , displacement sensor 19 delivers incremental displacement signals 20 to the counter of displacement determination device 18 . incremental displacement signals 20 can , for example , be generated by a hall sensor . the counter counts the pulses of the hall sensor until it is stopped . it is also possible to constitute incremental displacement signals 20 from the ripple of the armature current of the electric motor . the number of extremes of the rippled armature current is an indication of the displacement traveled . action 3 proceeds concurrently with action 2 . control arrangement 12 as shown in fig1 issues to positioning drive 10 the instruction to shift part 11 to the right at a specific speed . once position 2 has been reached , the counter for the displacement determination device is stopped . once this has happened , data set selection 14 then occurs in action 5 . the counter status is an indication of the distance between position 1 and position 2 . using the distance thus determined , it is possible , for example , to recognize a specific model of sun roof . for each model of sun roof , the spacings between position 1 and position 2 are known , as are the loads which occur for positioning drive 10 as a function of the model . parameter sets for specific sun roofs are stored in memory 13 as a function of distance . data set selector 14 applies an expanding tolerance band to the distance that is ascertained . data set selector 14 then searches for that data set 15 whose distance lies within the range determined . this data set 15 supplies control arrangement 12 with , for example , information about specific positions or load - dependent limit values . the reference run is thus complete , and positioning drive 10 is parameterized with data set 15 .