in fig1 , a power tool according to the invention being configured of a screw runner is shown and indicated generally by reference numeral 10 . the power tool 10 comprises a pistol - shaped housing 11 in which are received a motor , merely indicated by reference numeral 12 , a gearing and a controller 26 . the motor 12 drives , via a gearing not shown in detail , a drive shaft 14 intended to drive a tool , for example the bit of a screw runner . at the forward end of the housing 11 , facing the drive shaft 14 , there are provided a series of lighting elements 29 , such as leds , that radiate in forward direction and allow the working position to be illuminated ( in fig1 , a single led can be seen only ). at its lower end , the housing 11 comprises a pistol grip 16 , with a line cord 22 provided on the latter &# 39 ; s lower end for connection to a voltage source via a mains plug 24 . a trigger 18 is provided in the area of the “ pistol trigger ” for actuation of the motor 12 and the lighting elements 29 of the power tool . in a first switching state , the trigger 18 acts on a momentary - contact light switch , indicated as swlight in fig1 . when the trigger 18 is pressed down further to a second switching state , it additionally acts on a motor switch , likewise in the form of a momentary - contact switch and indicated as swstart in fig1 . further , a switch 20 , designed as momentary - contact switch and serving to reverse the power tool between clockwise and counter - clockwise rotation , and vice versa , is arranged on the top of the housing 11 . further , an indicator means 28 is provided in the forward upper area of the housing , for indicating that the power tool is running in counter - clockwise sense , which indicator may consist of one or more — for example flashing — leds . it is understood that the arrangement of the switching elements and of the lighting elements , as shown in the embodiment illustrated in fig1 , is shown by way of example only and that other arrangements may be preferred depending on the particular design and housing of the respective power tool . likewise , it is understood that the power tool 10 may also be designed as battery - driven power tool in which case it can do without the line cord 22 and the mains plug 24 , and a detachable battery pack may be provided at the lower end of the pistol grip 16 , for example . in the case of the power tool 10 , the controller 26 is designed as microprocessor - based control that controls all the functions of the power tool , such as the soft start function of the motor , braking of the motor when the power tool is switched off , overload protection , speed control and / or power control , if desired , and further testing and checking functions . the before - mentioned functions are , however , not part of the subject - matter of the present invention . the present invention relates to a novel way of setting the power tool to clockwise or counter - clockwise rotation . these different operating modes , and the way of setting them , will be described hereafter with reference to a flow chart shown in fig2 and indicated generally by reference numeral 30 . further , consideration should be given in this connection to a function table or truth table illustrated in fig3 . basically , the power tool 10 can be run in clockwise or counter - clockwise rotation by reversing the polarity of the motor 12 . now , the control 26 is designed so that the mode known as permanent clockwise rotation will be assumed in the basic condition , i . e . when the power tool 10 is started for the first time . that permanent clockwise rotation can be reversed to permanent counter - clockwise operation by actuation of a predefined combination of momentary - contact switches . further , the power tool can be operated a single time in the reverse direction of rotation , by operation of the clockwise / counter - clockwise rotation changeover switch 20 , provided the motor switch is actuated within a predefined time window . in fig2 , the setting state of the power tool to permanent clockwise rotation or permanent counter - clockwise rotation is defined by the value of variable dll . when dll = 1 , permanent counter - clockwise rotation is operative , i . e . the mode flag has been set . when dll = 0 , permanent clockwise rotation is operative . the direction of rotation of the drive shaft is defined by variable dir . in this connection , dir = 0 means that the drive shaft runs in clockwise sense , while dir = 1 means that it runs in counter - clockwise sense . the control 26 further comprises a counter - clockwise rotation timer which is activated by pressing the momentary - contact switch 20 . the timer value is defined by variable tll . when tll = 0 , the timer is switched off or the maximum time of the timer , for example 5 seconds , has elapsed . when tll = 1 , the timer has not elapsed yet . the design illustrated in fig2 makes additional use of a light switch indicated by swlight . swlight is actuated in a first switching stage by pressing down the trigger 18 . when the trigger 18 is pressed down further , the motor switch , indicated in fig1 by swstart , is actuated in addition to swlight . in fig2 , the decision flow is represented by lozenges as usual , the outputs being indicated by y and n , standing for “ yes ” or “ no ”. fig2 further makes use of the usual rectangular function blocks , and of a starting point and an end defining the logic beginning of the decision logic and / or the logic end of the decision logic . the combinations achievable with the decision logic according to fig2 are summarized in the truth table ( function table ) according to fig3 . the first line in that table means that when the motor switch swstart has been actuated , no permanent counter - clockwise rotation has been set and the timer has not been actuated or has elapsed , the power tool operates in clockwise rotation : dir = 0 . from the second line it can be derived that when the motor switch swstart has been actuated , no permanent counter - clockwise rotation has been set and the clockwise / counter - clockwise rotation changeover switch swrl has been actuated ( swrl = 1 ) and the timer has not elapsed yet ( tll = 1 ), the power tool operates in counter - clockwise rotation : dir = 1 . the third line of fig3 shows that when the motor switch swstart has been actuated , permanent counter - clockwise rotation is set and the timer has not been operated or has elapsed , the power tool likewise operates in counter - clockwise rotation : dir = 1 . in contrast , it can be derived from the last line that when the motor switch is actuated , permanent counter - clockwise rotation is set and the timer has been activated or has not elapsed yet , the power tool operates in clockwise rotation : dir = 0 . starting out from the basic condition dll = 0 ( permanent clockwise rotation ) or dll = 1 ( permanent counter - clockwise rotation ), the power tool can therefore be transferred to the respective preset permanent operating mode by pressing down the motor switch . or , alternatively , the clockwise / counter - clockwise rotation changeover switch swrl can be activated before the motor switch swstart is actuated . when the motor switch is then actuated within the predefined timer period of 5 seconds , the preset permanent direction of rotation will be changed over to the reverse direction of rotation for a single time . that behavior will now be described in more detail with reference to fig2 . once the decision logic has been activated at the start indicated by 32 , it is initially inquired , at branch 34 , if the light switch swlight has been activated by operation of the trigger 18 . if this is the case , the right - hand output from branch 34 applies . it is then inquired at branch 38 if the clockwise / counter - clockwise rotation changeover switch swrl has been actuated in addition to the light switch . if this is the case , a predefined permanent counter - clockwise or permanent clockwise direction of rotation is reversed to the reverse direction of rotation , which is stored . this is taken into consideration , and stored , by the microprocessor using a “ mode flag ”. the resulting indication at box 42 is dll =! dll , the “!” representing a negation , i . e . a logic not . after reversal of the permanent direction of rotation in box 42 it is inquired at branch 44 if the clockwise / counter - clockwise rotation changeover switch swrl has been released again . if this is the case , it is determined by the next inquiry 46 if the motor switch has been actuated . when swrl has not been released again , the system waits until this has happened , as indicated by the feedback loop . when it is determined at branch 34 that the light switch has not been activated , it is first determined at branch 36 if the clockwise / counter - clockwise rotation changeover switch swrl has been additionally actuated . when it has not , the right - hand output directly leads to the next branch 46 , i . e . the inquiry if the motor switch has been actuated . however , when the clockwise / counter - clockwise rotation changeover switch swrl has been actuated , the timer is started at block 40 , and the output leads to the next branch 46 . at branch 46 it is now determined if the motor switch swstart has been actuated . if swstart has not been actuated , the left - hand output of the branch directly leads to the end 56 ( stop ). however , when the motor switch is actuated , the output of branch 46 leads to the next branch 48 . now , when permanent counter - clockwise operation has been set , the timer has been actuated and has not elapsed yet ( dll and tll ), the left - hand output results , i . e . the preset permanent counter - clockwise rotation is reversed to clockwise rotation , which is indicated as clockwise rotation in block 50 ( dir = 0 ). the timer is then reset at block 54 ( tll = 0 ), and the process ends at 56 . in contrast , when it is determined at branch 48 that the logic combination of permanent counter - clockwise rotation dll and activated and still active timer tll is not true , then the right - hand output results so that the power tool is operated in counter - clockwise rotation , as indicated at box 52 by dir = 1 . the timer is then stopped at box 54 , and the process ends at 56 . as an alternative to that inquiry ( dll and tll ), the logic expression (! dll and ! tll ) is further inquired via a logic or operation . the inquiry , therefore , is whether permanent counter - clockwise rotation has been set and the timer has not been actuated or has elapsed . if this is true , the power tool is operated in clockwise rotation and the left - hand output to box 50 applies . if this is not true because , for example , permanent counter - clockwise rotation has been set and the timer has not been actuated or because permanent clockwise rotation has been set and the timer has been actuated and has not elapsed yet , the right - hand output to box 52 applies ; the power tool is operated in counter - clockwise rotation . preferably the controller 26 is configured programmable , e . g . it may be configured as a microprocessor based controller . the decision logic tree according to fig2 will be run periodically every 1 to 10 milliseconds .