DUDEK Emil: Remove the screw from the rear and the one inside the battery compartment. The back section will lift off after a bit of gentle persuasion - hinge it from the top where the power socket sits Logic comments: [C] clears the last number entered and (AC) clears the whole calculator. Input overflow is suppressed, inputting an eleventh digit is ignored. There is selectable constant on multiply and divide only by double hitting the operator; i.e. [5][X][X][=] gives ‘25’ [=] gives ‘125’ etc. Negative numbers are shown by a minus sign in the digit to the immediate left of a number but as there is no eleventh digit to travel into you are limited to nine digit negative numbers. Divide by zero shows ‘E’ in the first (far right) digit and is not recoverable using. Overflow shows ‘E’ in the first (far right) digit and is not recoverable using. Memory store is not indicated - you have to remember it! Memory overflow will result in an error and zero the memory. Negative square roots are allowed and result in a negative number. There is a switch selecting 6,4,3,2,1,0 fixed decimal points. Another switch selects between floating decimal point [F], fixed round down [CUT] and fixed round [5/4]