The device and the adapter according to the invention with the characteristics of the independent claims have therefore the advantage that the measuring beam that is send by the sending device and/or the receiving area of the receiving device can be redirected by the redirecting device, whereby it is possible to carry out a length measurement in two direction without having to move the device. 
Therefore the redirecting device can be arranged in a first position in such a way that it does not influence the measuring beam that is send by the sending device nor the receiving area of the receiving device.  Then a length measurement can be carried out in a first direction (forwards) by the device or a device that is accommodated by the adapter. 
Subsequently the redirecting device is arranged in a second position in such a way that it redirects the measuring beam that is send out by the sending device as well as the receiving area of the receiving device in a second direction.  Without having to move the device a length measurement can now be carried out in a second direction, which is provided by the arrangement of the redirecting device (sideways).  A measurement that is carried out “sideways” means hereby a measurement that deviates from the first direction; that can be a measurement to the right, left, upwards or downwards, which means redirected by 90°, but also a measurement in a direction that does not stand vertical on the first direction but encloses with it another angle (for example 45°). 
The redirecting of the optical measuring beam can also be used to adjust the device to a reference point (for example the ground or the top) without carrying out a measurement in that direction.  The optical measuring beam can for example at first be redirected upwards by the redirecting device so that it is possible to position the device according to the invention or the adapter according to the invention below a reference point that is given at the top of a space.  Subsequently the redirecting device is removed or moved in such a way that the optical beam is not redirected upwards anymore by the redirecting device.  A length measurement can now be carried out along the first direction, whereby the device measures from a specific reference point. 
In a preferred embodiment the redirecting device is connected movably with the housing of the device or with the frame of the adapter.  This enables a simple arrangement of the redirecting element in the first position, in which it does not influence the measuring beam that is send out by the sending device nor the receiving area of the receiving device, as well as in the second position, in which it redirects the measuring beam that is send out by the sending device and/or the receiving area of the receiving device in the second direction.  Also the alternation of the redirecting element between the two positions is thereby simplified without the danger that the device is moved. 
In a particularly preferred embodiment the redirecting device provides a sled and the housing of the device or the frame of the adapter provides at least one guiding element for guiding the sled.  Thereby the redirecting element can be moved between the two positions without a high resistance. 
In a further preferred embodiment the redirecting device provides a mirror or a prism or another redirecting element that qualifies for the wave length of the optical measuring beam. 
In a further preferred embodiment the device or the adapter provides a level or a similar element for a horizontal alignment of the device.  This is in particular necessary if a reference point has to be targeted at the top with the redirected optical measuring beam based on which a length measurement shall take place. 
At usual electroscopic devices for a length measurement the length measurement takes usually place from a reference plane of the device.  That can be determined by the back or front end of the device, or also by an attachment possibility for a tripod in the middle of the device.  The used reference plane can be adjusted at the device, so that the result of the length measurement that is shown by the device illustrates the length that has been determined based on the reference plane. 
At a measurement “sideways” along the second direction by redirecting the optical measuring beam and the receiving area of the measuring optic the length should preferably be measured from the redirecting point of the optical measuring beam at the redirecting device up to the measuring object.  Therefore the offset has to be subtracted from the actually determined length, which results thereby in that the optical measuring beam runs at first a little along the first direction “forwards” up to the redirecting device.  Preferably this consideration of the offset takes place automatically if the device detects with the aid of a position detector at the device or the adapter that the redirecting direction is located in the second position, in which it redirects the measuring beam that has been send out by the sending device as well as the receiving area of the receiving device in the second direction.  But it is also possible to activate the consideration of the offset manually at the device. 
In a further preferred embodiment the device or the adapter provides a mechanic measuring device, with which a length measurement can also be carried out.  The mechanic measuring device allows for example a length measurement along the outside of a measuring object, if the length that has to be measured is not limited by a measuring area, which scatters the measuring beam at least partially back to the device. 
The mechanic measuring device can for example be a measuring tape or a link measuring stick and can be arranged at the side of the device or the adapter. 
The mechanic measuring device also allows to carry out a length measurement in a direction while the optical measuring beam is redirected by the redirecting device and is for example used to target a reference point based on which the measurement shall take place. 
In a further preferred embodiment the mechanic measuring device is connected with the housing of the device or the frame of the adapter in a movable way (for example rotatable or foldable), so that the direction, in which the measurement with the mechanic measuring device shall take place, can be changed. 
In a further preferred embodiment the length that has been measured with the mechanic measuring device can be read automatically (for example with the aid of a magnetic or an optical code on the measuring stick or on the barrel of the measuring tape) and be illustrated on a display element of the device.  The adapter according to the device provides therefore an interface for transmitting the measured length to the device that is accommodated in the adapter. 
In a further preferred embodiment of the adapter it provides at least one holding element for holding the device for the length measurement.