Scientific calculator

A scientific calculator includes a conversion table memory for storing as a conversion table a combination of each kind of conversion equation and a selection number, a key board providing numeric keys and a specific key, a numeric value memory for storing the entered numeric values, a mode setting section for setting the current mode to a conversion mode, a designating section for designating the selection number during conversion mode, reading section for reading from the conversion table the conversion equation corresponding to the designated selection number, a conversion section for converting the numeric value stored in the numeric value memory from one unit to another on the basis of the read conversion equation, and a display section for displaying the converted numeric value.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to scientific calculators, and more 
particularly to a scientific calculator capable of converting one unit 
into another. 
2. Description of the Prior Art 
Conventional scientific calculators include a calculator capable of 
converting a numeric value entered with a certain unit into a numeric 
value with a different unit. For example, some calculators designed for 
scientific calculations are provided with a unit conversion function to 
perform a conversion calculation of physical units. Some calculators 
designed for travelers are capable of converting one currency unit into 
another. 
Since scientific calculators, which are a small size electronic device, 
have only a limited number of keys, unit conversion functions are 
incorporated in keys for entering numeric values with the result that the 
unit conversion functions are performed by operating keys for entering 
numeric values 0 to 9 following the depression of a secondary function 
designation key ([2ndf] key). 
FIG. 7 is a view illustrating an external configuration of a scientific 
calculator in the prior art. As shown in FIG. 7, this method permits 
storing 10 function units with a combination of [2ndf] key and numeric 
value keys. 
Referring to FIG. 7, Reference Numeral 81 designates a display unit of the 
calculator, 81a a numeric value display unit for displaying numeric 
values, and 81c a [2ndf] symbol indicating the selection of a secondary 
function. 
Reference Numeral 82 designates a key input unit, 82a a unit conversion 
calculation key assigned as the secondary function of numeric value 
entering keys, which includes such keys as [in.fwdarw.cm], and 
[cm.fwdarw.in] keys, 82b a [2ndf] key for designating the secondary 
function, 82c a [ON/C] key for clearing calculations or turning on the 
calculator that has been turned off, 82d a key for performing function 
calculations, which includes such keys as [sin], [cos] keys and the like, 
82e an argument key for entering numeric values, which includes such keys 
as [0] key through [9] key, 82f a key for designating the kind of 
calculations such as addition, subtraction, multiplication and division, 
which includes such keys as [+], [-], [.times.], and [.div.] keys, 82g a 
key for performing memory calculations, which includes such keys as 
[X.fwdarw.M], [RM], [M+] keys, and 82h a [=] key for performing 
calculations such as addition, subtraction, multiplication and division. 
FIG. 8 is a view illustrating a calculation example of unit conversion by a 
conventional scientific calculator. In the example shown in FIG. 8, the 
inch unit in 1.23 inches is converted into the centimeters. 
Step 901: Step 901 clears the content of the calculator by operating the 
[ON/C] key. 
Step 902: Step 902 enters 1.23 whose unit is to be converted. 
Step 903: Step 903 selects the secondary function. In this operation, the 
secondary function described above the key switch will be made effective. 
Step 904: Step 904 performs a conversion calculation. Operating [0] key 
performs the calculation of [in.fwdarw.cm], which is provided as a 
secondary function of [0] key. 
However, it is impossible to assign many calculation conversion functions 
to numeric value entering keys whose number is restricted. Consequently, 
incorporating conversion calculation functions in excess of the number of 
numeric value entering keys has a drawback which demands either assigning 
the conversion functions to other keys than numeric value entering keys or 
increasing the number of functions assigned to numeric value entering keys 
as a tertiary or a quaternary function. 
Thus, in either case, conventional calculators have a drawback that the 
number of conversion calculations depends on the number of keys. 
As additional related art of the present invention a small size electronic 
calculator is known as disclosed in Japanese Laid-Open Patent Publication 
No. SHO 58-178459/1983. The calculator provides a plurality of unit keys 
and a memory for storing conversion values between units designated by the 
unit key to perform initialization of the conversion value to be stored in 
the memory by operating a unit key and to perform the unit conversion 
processing by using the conversion value stored in the memory. A unit 
conversion device is also disclosed in Japanese Laid-Open Patent 
Publication No. SHO 62-166551/1987, the device permitting the conversion 
between units in a combination of units absent in a memory of the device 
by storing a plurality of conversion rates in the memory so that the 
conversion rates can be used. 
SUMMARY OF THE INVENTION 
The present invention provides a scientific calculator that permits easily 
selecting a plurality of conversion calculations without being restricted 
by the number of keys either by adopting a method that allows selecting a 
plurality of unit conversion calculations by incorporating in an ordinary 
calculator a key exclusively used for unit conversion ([conv] key) 
specifying a unit conversion function so that such key can be combined 
with numeric value entering keys([0] key to [9] key) conventionally 
incorporated in the ordinary calculator, or by adopting a method which 
offers a guidance display by adding an exclusive symbol ([?]) in a date 
and numeric value display originally incorporated in the ordinary 
calculator for displaying the result of unit conversion calculations. 
The present invention provides a scientific calculator having a scientific 
calculation mode for performing a scientific calculation and a conversion 
mode for converting a numeric value from one unit to another, said 
calculator comprising: conversion table storage means for storing as a 
conversion table a combination of each kind of conversion equation for 
converting a numeric value from one unit into another and a selection 
number attached to each conversion equation; key input means including 
numeric keys for entering a numeric value and a specific key for setting a 
mode to the conversion mode: numeric value storing means for storing the 
entered numeric value; mode setting means for setting the current mode to 
the conversion mode by pressing the specific key; designating means for 
designating the selection number in the conversion table during the 
conversion mode; reading means for reading from the conversion table the 
conversion equation corresponding to the designated selection number; 
conversion means for converting the numeric value stored in the numeric 
value storing means from one unit to another on the basis of the read 
conversion equation; and display means for displaying the converted 
numeric. 
In accordance with the present invention, entering a predetermined 
selection number by the input means with the specific number displayed 
permits the calculation means to calculate the conversion calculation with 
the selected number.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention will be detailed in connection with a preferred 
embodiment shown in the drawings, but the embodiment is not intended to 
limit the scope of the invention. 
The present invention can be applied to each kind of calculator, 
specifically scientific calculator both large and small, but the invention 
is particularly suitable for a pocket-size scientific calculator capable 
of function calculations. 
The present invention will be detailed with respect to a pocket-size 
scientific calculator capable of function calculations. The present 
invention can be applied by adding a constituent requirement of the 
invention to a scientific calculator provided with basic functions of an 
ordinary calculator of this type. 
In accordance with the present invention, key input means and the 
designating means are used as the input devices such as a keyboard, a 
pointing device, a touch sensor and an optical character reader. 
As the mode setting means, the reading means and the conversion means, it 
is convenient to use a microcomputer comprising a CPU, a ROM, a RAM and an 
I/O port. As the conversion table storage means, a ROM in the 
microcomputer is used and as the numeric value storing means, a RAM in the 
microcomputer is used. 
As display means, display devices such as a LCD device (liquid crystal 
display device), and an EL display devices are used. 
FIG. 1 is a block diagram illustrating a construction of one embodiment of 
applying the present invention to a 10-digit decimal display scientific 
calculator. In FIG. 1, Reference Numeral 1 designates a CPU for 
controlling the calculator, 2 a ROM for storing a program and constants 
for use in operating the calculator, 3 a RAM used for controlling the 
calculator and as a numeric value memory, 4 an LCD driving circuit for 
controlling the LCD drive, 5 an LCD display unit for displaying numeric 
values and symbols, 6 a key matrix for detecting a key input. 
In ROM 2 are stored a conversion calculation table, a [conv] key processing 
program, a numeric value key processing program, and a conversion 
calculation program. RAM 3 comprises convflag 1, convflag 2, buffer 1, and 
buffer 2. 
Flags will be detailed hereinbelow (refer to FIGS. 3 and 4). 
Convflag 1: convflag 1 memorizes set/reset states (1 bit construction). It 
is set by operating [conv] key to hold the set state during a conversion 
calculation. In other words, it indicates that the conversion calculation 
mode has been selected to set the calculator in a state of waiting for the 
input of a number (numeric value) in the first digit. 
Convflag 2: convflag 2 memorizes set/reset states (with 1 bit 
construction). Input of a number (numeric value) in the first digit has 
been completed to set the calculator in a state of waiting for the input 
of a number (numeric value) in the second digit. In other words, it 
indicates a state of waiting for the input of a number (numeric value) in 
the second digit after completing the input of the first digit number. 
Then, the buffers will be detailed hereinbelow (refer to FIGS. 3 and 4). 
Buffer 1: buffer 1 memorizes one numeric value (it is possible to memorize 
numeric values 0 through 9 with 4 bit construction). It memorizes a number 
(numeric value) in the first digit. 
Buffer 2: buffer 2 memorizes (it is possible to memorize numeric values 0 
through 9 with 4 bit construction). It memorizes a number (numeric value) 
in the second digit. 
FIG. 2 is an external view illustrating one embodiment in which the present 
invention is applied to a 10-digit decimal scientific calculator. In FIG. 
2, a scientific calculator capable of performing 98 kinds of conversion 
calculations only by adding a 10-digit display unit, and a [conv] key and 
a [?] symbol as an argument key. 
Reference Numeral 31 designates a display unit of the calculator, 31a a 
date and numeric value display unit, 31b a [?] symbol used for forming a 
guidance display at performing conversion calculations, and 31c a [2ndf] 
symbol for designating the state of the secondary function selection. 
Reference Numeral 32 designates a key input unit, 32a a [conv] key 
(conversion)for designating a conversion calculation mode, 32b a [2ndf] 
key (2nd function) for designating the secondary function, 32c a [ON/C] 
key, 32d a key for performing functions, which includes such keys as 
[sin], [con] and the like, 32e an argument key for entering numeric values 
such keys as [0] key through [9] key, 32f a key for designating four kind 
of calculations such as addition, subtraction, multiplication and 
division, which includes [+], [-], [.times.], and [.div.] keys, 32g a key 
for memory calculations, which includes such keys as [X.fwdarw.M], [RM] 
and [M+] keys. 
FIG. 3 is a flowchart showing a function processing at a [conv] key for 
designating a unit conversion calculation mode in accordance with the 
present invention. 
Step 401: Step 401 judges convflag 1 either to allow the process to proceed 
to Step 405 and Step 406 or to proceed to Step 402 through Step 404. When 
it is judged that the flag has been set or a conversion calculation mode 
has been selected, the process proceeds to Step 405 and Step 406. When it 
is judged that the flag has been reset, the process proceeds to Step 402 
through 404. 
Step 402: Step 402 sets convflag 1 to select a conversion calculation mode. 
Step 403: Step 403 allows the calculator to display 01-99 [] at the date 
and numeric value display unit. 
Step 404: Step 404 uses [?] symbol to display a guidance. 
Step 405: Step 405 brings back the display to the state immediately before 
performing the conversion calculation. 
Step 406: Step 406 resets convflag 1 and convflag 2. 
FIG. 4 is a flowchart showing a function processing of numeric value keys 
in accordance with the present invention. In FIG. 4 the following steps 
are detailed. 
Step 501: Step 501 judges convflag 1 so that when the flag has been set, 
the process proceeds to Step 502 whereas when the flag has been reset, the 
process proceeds to Step 512 to perform respective processing. 
Step 502: Step 502 judges convflag 2 so that when the flag has been set, 
the process proceeds to Step 503 whereas when the flag has been reset, the 
process proceeds to Step 509 to perform ordinary processing respectively. 
Step 512: Step 512 functions when convflag 1 has been reset. At this point, 
since a conversion calculation has not been selected, an ordinary numeric 
value input is performed. 
Step 509 through step 511: Step 509 through Step 511 functions when 
convflag 1 has been set and convflag 2 has been reset. At this point, the 
first digit number for a conversion calculation is entered. The entered 
numeric value is memorized in buffer 1. Additionally, the entered numeric 
value is displayed for guidance to enable users to confirm it. These steps 
set convflag 2 to indicate that the input of the first digit number has 
been completed. 
Step 509: Step 509 allows the calculator to store the entered numeric value 
in buffer 1 on RAM 3. 
Step 510: Step 510 allows the calculator to display the entered numeric 
value at a cursor () position of LCD 5 via a LCD driving circuit shown in 
FIG. 1. 
Step 511: Step 511 sets convflag 2 to set the calculator in a state of 
waiting for the input of a numeric value in the second digit. 
Step 503 through 508: Steps 503 through 508 functions when convflag 1 has 
been set and convflag 2 has been set. These steps allows entering the 
second digit number of conversion calculation and performing a calculation 
conversion corresponding to the number. 
Step 503: Step 503 allows the calculator to memorize the entered numeric 
value in buffer 2 on RAM 3. 
Step 504: in the same manner as Step 510, Step 504 allows the calculator to 
display the entered numeric value at the cursor () position of LCD 5. 
Step 505: Step 505 allows the calculator to display the entered numeric 
value temporarily so that users can confirm it. In other words, it is 
displayed for 0.3 second. 
Step 506: Step 506 performs a conversion calculation corresponding to 
numbers memorized in buffer 1 and buffer 2. ROM 2 shown in FIG. 1 
memorizes the procedure in advance. Additionally, in ROM 2, there is 
provided a table (conversion table) showing a conversion calculation 
equation corresponding to the second digit shown in FIG. 6. The program 
functions to permit the calculator to display the conversion calculation 
corresponding to the second digit number by referring to the table. 
Step 507: Step 507 allows LCD 5 to displays the result of the calculation 
in the similar manner as step 510. 
Step 508: Step 508 resets flags, convflag 1 and convflag 2 to return to a 
normal calculation state as a post-calculation processing. 
FIG. 5 is a view illustrating a calculation example of a unit conversion in 
the scientific calculator in accordance with the present invention. This 
particular example performs a process of converting 1.23 in (inches) into 
the cm's (centimeters). 
Step 601: Step 601 cleared the content of a calculator with [ON/C] key 
operation. 
Registers and flags used for calculations in RAM 3 in FIG. 1 are cleared to 
display "0" via a LCD driving circuit. At this point, convflag 1 and 
convflag 2 are reset. 
Step 602: Step 602 allows entering 1.23 a numeric value to be converted. 
Upon detecting a numeric value key input with key 6 shown in FIG. 1, the 
calculator performs a processing shown in Step 501 through 512 shown in 
FIG. 4 to enter a numeric value since the convflag has been reset in each 
key input operation. 
Step 603: Step 603 selects a conversion calculation mode. 
Symbol [?] denotes a guidance that promotes a number input whereas numeric 
representation 01-98 designates that a numeric value ranging from 01 
through 98 can be entered. Then the underlined portion within [] 
represents a cursor display, which indicates that a numeric value to be 
entered will be entered at the cursor position, namely at the first digit 
of the number. 
Upon detecting a [conv] key input with key 6 shown in FIG. 1, the 
calculator performs a processing shown in Step 401 through 404 shown in 
FIG. 3 since the convflag has been reset in each key input operation, 
thereby performing a guidance display shown in a display unit. At this 
point, convflag 1 is set. 
Step 604: input of the number on the first line 
Step 604 selects and enter Number `01` corresponding to the conversion 
calculation of in.fwdarw.cm from FIG. 6. At this point, convflag 1 has 
been set and convflag 2 has been reset. In FIG. 4, a processing from Step 
501.fwdarw.Step 502.fwdarw.Step 509.fwdarw.Step 510 is performed to 
display the number on the first line. At this point, Step 511 sets 
convflag 2. 
Step 605: Step 605 allows entering a numeric value in the second digit. 
By entering the number in the second digit, the entered numeric value is 
temporarily displayed. At this point, both convflag 1 and convflag 2 have 
been set, Step 501 through Step 505 shown in FIG. 4 are performed to 
temporarily display the entered numeric value. 
Step 606: Step 606 allows performing a conversion calculation. 
After temporarily displaying the numeric value entered at Step 605, a 
conversion calculation corresponding to the input number is performed to 
display the result on a date and numeric value display unit (LCD 5). At 
this point, in FIG. 4, subsequent to Step 505 the processing from Step 506 
through Step 508 is executed to perform the conversion calculation, 
thereby displaying the result of the calculation. 
FIG. 6 is a view showing a conversion table in the scientific calculator in 
accordance with the present invention. Referring to FIG. 6, there is shown 
a correspondence of a 2-digit decimal numeric values identical to 
respective unit conversion calculation. Consequently, entering the 2-digit 
decimal numeric value subsequent to a [conv] key operation allows 
performing a conversion calculation corresponding to the number column. 
[conv] 01: in.fwdarw.cm (conversion of the inches into the centimeters) 
[conv] 02: cm.fwdarw.in (conversion of the centimeters into the inches) 
[conv] 98: g.fwdarw.oz (conversion of the grams into the ounces) 
Only adding to an ordinary calculator a key exclusively used for 
designating a unit conversion calculation and a symbol display exclusively 
used for displaying a designation key for designating a unit conversion 
permit performing a plurality of conversion calculations only with numeric 
number entering keys without depending on the number of keys.