Dual-function keys for sign change and correction of erroneous entries

Claim 2

rIn a calculator having digit keys and a decimal point key, and a register for storing digital information, the combination of a. means responsive to depression of said digit keys to enter corresponding information in said register, b. storage means containing information representative of the sign of the digital information stored in the register, c. a bistable device normally in a first state and settable to a second state in response to depression of said decimal point key, and d. means operable when said bistable device is in said second state and effecting a change in the contents of said sign storage means in response to depression of said decimal point key.

Claim 3

The combination of claim 1, wherein said sign change means comprises means to complement the information in said sign storage means.

Claim 4

The combination defined in claim 2, further including a new entry detector settable from a first state to a second state indicative of entry of a new number, and wherein a complementation of the contents of said sign storage means occurs in response to depression of said decimal point key with both said bistable device and said entry detector in said first states.

Claim 5

The combination defined in claim 2, further including a new entry detector settable from a first state to a second state indicative of entry of a new number, and wherein a complementation of the contents of said sign storage means occurs in response to depression of said decimal point key with both said bistable device and said entry detector in said second states.

Claim 6

The combination defined in claim 2, further including a new entry detector normally in a first state and settable to a second state indicative of entry of a new number, and wherein a complementation of the contents of said sign storage means occurs in response to depression of said decimal point key with both said bistable device and said entry detector in said first states and alternatively in response to depression of said decimal point key with both said bistable device and said entry detector in said second states.

Claim 7

The combination defined in claim 1, wherein the contents of said sign storage means are normally representative of a positive sign and said sign change means change the contents of said sign storage means to information representative of a negative sign.

Claim 8

The combination defined in claim 6, wherein said bistable device is a first one of two bistable devices and said sign storage means comprises the second bistable device, said second bistable device being normally in a first state representative of a positive sign and being settable to a second state reresentative of said negative sign when said first bistable device is in its second state and in response to said decimal point key depression.

Claim 9

The combination defined in claim 6, further including a new entry detector normally in a first state and settable to a second state indicative of entry of a new number, and wherein entry of said negative sign in said sign storage means is responsive to depression of said decimal point key with said bistable device in its second state and said new entry detector in its first state and is responsive alternatively to depression of said decimal point key with both said bistable device and said new entry detector in said second states.

Claim 10

The combination defined in claim 6, further including a new entry detector normally in a first state and settable to a second state indicative of entry of a new number, and wherein said negative sign change occurs in response to depression of said decimal point key with said bistable device in said second state and said new entry detector in said first state.

Claim 11

The combination defined in claim 9, wherein said sign change means includes means to complement the contents of said sign storage means in response to depression of said decimal point key with both said bistable device and said new entry detector in their first states and alternatively in Response to depression of said decimal point key with both said bistable device and said new entry detector in their second states.

Claim 12

The combination defined in claim 6, further including a new entry detector normally in a first state and settable to a second state indicative of entry of a new number, and wherein entry of said negative sign in said sign storage means is responsive to depression of said decimal point key with said bistable device in its second state and said new entry detector in its first state.

Claim 13

The combination defined in claim 11, wherein said sign change means include means to complement the contents of said sign storage means in response to depression of said decimal point key with both said bistable device and said entry detector in said first states.

Claim 14

The combination defined in claim 11, wherein said sign change means complement the contents of said sign storage means in response to depression of said decimal point key with both said bistable device and said entry detector in said second states.

Claim 15

The combination of claim 6, wherein the calculator has function control keys, including a ''''Total'''' key for commanding a total-taking operation, and said register is clearable when a clear signal is generated, and further including a new entry detector normally in a first state and settable to a second state indicative of the entry of a new number into said register, normally disabled means for generating a signal to clear the register, means responsive to the second state of said new entry detector and operable to disable said total-taking command and to enable said clear signal generation means in response to depression of said ''''Total'''' key, and means to change the contents of said sign storage means to said normal positive sign in response to said clear signal.

Claim 16

The combination of claim 14, further including means operable to set said new entry detector to said first state in response to said clear signal, and wherein said disabling and enabling means comprise a further bistable device normally in a first state and settable to a second state in response to the second state of the new entry detector, said total-taking command being disabled and said clear signal being enabled in response to said further bistable device in said second state.

Claim 17

The combination of claim 15, further including means providing a signal upon overflow from said register, and wherein said further bistable device is alternatively settable to its second state in response to said overflow signal.

Claim 18

The combination defined in claim 1, further including means for storing information as to the location of the decimal point relative to the digits stored in said register, said means being responsive to depression of said decimal point key.

Claim 19

The combination defined in claim 17, wherein said calculator has at least one function key and said decimal point location storing means are alternatively responsive to depression of said function key when said bistable device is in said first state and are operable to effect storage of said decimal point location information.

Claim 20

The combination defined in claim 18, further including a new entry detector normally in a first state and settable to a second state indicative of entry of a new number, and means operable when said new entry detector is in said first state and effective to set said bistable device to said first state and to store a particular sign in said sign storage means in response to depression of a said digit key and alternatively in response to depression of said decimal point key.

Claim 21

The combination of claim 19, wherein setting of said new entry detector to said second state occurs in response to depression of a said digit key and alternatively in response to depression of said decimal point key.

Claim 22

The combination defined in claim 20, wherein depression of said function key sets said new entry detector to said first state.

Claim 23

The combination of clAim 17, wherein said sign change means complement the information in said sign storage means.

Claim 24

The combination defined in claim 22, wherein said calculator has at least one function key and said bistable device is settable to said second state when said bistable device is in said first state and in response to depression of said decimal point key and alternatively in response to depression of said function key.

Claim 25

The combination defined in claim 22, further including a new entry detector normally in a first state and settable to a second state indicative of entry of a new number and wherein said sign change means complement the contents of said sign storage means alternatively when said decimal point key is depressed with said new entry detector in its first state.

Claim 26

The combination defined in claim 24, wherein said decimal point storing means are responsive to depression of a said digit key when said bistable device is in said second state and said new entry detector is in said first state.

Claim 27

The combination defined in claim 25, wherein said decimal point location storing means are alternatively responsive on to depression of said decimal point key when said bistable device is in said first state and said new entry detector is in said second state.

Claim 28

The combination defined in claim 26, wherein setting of said new entry of detector is set to said second state occurs in respones to depression of a said digit key.

Claim 29

The combination defined in claim 26, wherein said calculator has at least one function key and said decimal point location storing means are alternatively responsive to depression of said function key when said bistable device is in said first state.

Claim 30

The combination defined in claim 26, wherein said decimal point location storage means are alternatively responsive to depression of a decimal point key with said bistable device in said second state and said new entry detector is in said first state.

Claim 31

The combination defined in claim 29, wherein setting of said new entry detector to said second state occurs in response to depression of a said digit key.

Claim 32

The combination defined in claim 30, wherein said claculator has at least one function key, and said decimal point location storage means are alternatively responsive to depression of said function key with said bistable device in said first state.

Claim 33

The combination defined in claim 31, wherein setting of said new entry detector to its second state occurs in response to depression of a said digit key and alternatively in response to depression of said decimal point key with said bistable device in the second state.

Claim 34

In a calculator having digit keys and function control keys, including a ''''Total'''' key for commanding a total-taking operation, and a register storing digital information, the information being clearable when a clear signal is generated, the combination of a new entry detector normally in a first state and settable to a second state indicative of the entry of a new number into said register, normally disabled means for generating a signal to clear the register, and means responsive to the second state of said new entry detector and operable to disable said total-taking command and to enable said clear signal generation means in response to depression of said ''''Total'''' key.

Claim 35

In a calculator having digit keys and function control keys, including a ''''Total'''' key for commanding a total-taking operation, and a register storing digital information, the information being clearable when a clear signal is generated, the combination of a new entry detector normally in a first state and settable to a second state indicative of the entry of a new number into said register, normally disabled means for generating a signal to clear the register, and means responsive to the second state of said new entry detector and operable to disable said total-taking command and to enable said clear signal generation means in response to depression of said ''''Total'''' key.

Claim 36

The combination of claim 33, further including means operable to set said new entry detector to said first state in response to said clear signal, and wherein said disabling and enabling means comprise a bistable device normally in a first state and settable to a second state in response to the second state of the new entry detector, said ''''total-taking'''' command being disabled and said clear signal being enabled in response to said bistable device in said second state.

Claim 37

The combination of claim 34, further including means providing a signal upon overflow from said register, and wherein said bistable device is alternatively setTable to its second state in response to said overflow signal.