Command and Answer Memories

Napier automatically keeps the last 10 commands and answers for reuse. Each time you tap the ENTER (or DataIn) key, both the expression being evaluated and the result are added to the top of the list and the one on the bottom dropped off. You may find that youíd like to use an answer you got previously in the expression you are working on later. To do this, tap the ANS key in the row of memory access keys below the information box. A list of the 10 previous answers will drop down, and you can pick one by tapping it.

Now if you tap the second one, A2, (the total amount of the bill including tip), you will get the following:

The reference to the answer for use in the new expression is A2, not the value itself, similarly to the representation of a memory by M2 rather than the value, and for similar reasons. This will be discussed more below when we get into reusing expressions.

The Val symbol

As we discussed above, if you continue with a previous answer when starting an expression, the Val symbol will appear in the expression, but if you start a new expression it wonít. What is actually going on, is that the previous answer is saved with each expression, weather it appears or not, and can be reused anywhere in the expression. Napier will keep it in the expression if you enter an operator such as +, because it is guessing that you want to continue with the previous answer. However, if you enter something like a number, the guess is that you are starting a new expression, unrelated to the previous answer. You can still easily use the previous answer though.

For example, if you evaluate an expression 1.5^.5 (the square root of 1.5), then want to divide 4.5 by that number, hereís how to do it. First evaluate the 1.5^.5 which will give you 1.2247_, then start typing the next expression by entering 4.5/. When you enter the 4, the previous answer will disappear because you didnít enter an operator such as +, so the guess was you were starting a new expression. After you enter the / character (division), you need to get the previous answer, so press the Val key which will enter the Val symbol. If you then tap ENTER, the result is 3.6742_

At this point, you may well be wondering what the difference is between Val and A1 (the 1^st previous answer value). That brings us to the oft-promised discussion of saving and reusing commands.

Reusing Commands ñ Command and History Memories

At the simplest level, command reuse can be treated like the ìKî key that appears on some calculators, a constant to be used, sometimes with an operation, on subsequent entries. For example, if you want to multiply a succession of values by pi, first tap the pi key, then the * (multiplication) key. Now, before entering the first value you want to multiply by pi, tab the CIn key (above the Val key). This stores the current expression as entered in the first command memory C1.

To use this saved command, tap the C1 key (above the CIn key) and the contents of the C1 command memory will be put into the command bar. Then just enter the number you want to multiply by pi and hit enter. Keep doing the same for other numbers, tap C1, enter the next number, tap ENTER.

This is what it looks like after loading C1 with CIn, then tapping the C1 key.

As a bit of a digression at this point, if you are doing something like this, creating a series of results, there are two ways to look back over what happened. If there are less than 10 answers, just tap the Ans key (discussed above) and it will show the last 10 answers. If you want a more permanent record, with up to 1000 entries, rather than using the ENTER key, use the DataIn key. This will append each result to the Data Set, which you can view using the DView function under the Data dropdown. To delete everything in the Data Set to restart, use the DDel function. This will all be discussed more below.

Why the cursor position is also saved

This is what the command dropdown looks like with a few saved commands:

If the command was saved with the cursor other than at the end of the expression, an @ sign is displayed in the command, showing the cursor position.

If you are evaluating a series of numbers in an expression like (1 ñ Sin(#)) ^ 2, where the # represents the numbers to be used,  it is a lot easier to save the command with the cursor at the insert position. That way, you just tap the C1 key, enter the next number, then tap ENTER. It avoids having to reposition the insertion point each time, although that will work also.

These saved commands are part of the saved state (discussed below), so you can have different sets of saved commands for each of the different environments accessed via the save / read state operations.

Much more complex user defined functions can be added by using the VBScript programmability. This is discussed more below.

Automatically saved History

As discussed above, the last 10 answers and expressions are automatically saved, you can reuse a previous answer with the Ans key. You can also reuse the commands, which you access with the Hist dropdown key just below the information box. This shows the same list as the Ans dropdown, but when you tap on one, rather than a reference to an answer being inserted into the expression, the previous command replaces whatever was in the command box. At this point you can either just immediately execute it, continue editing it, save it in one of the command memories, or whatever.

For convenience, there is an H1 key, just below the Val key, which recalls the last executed command. This is identical to the H1 in the Hist dropdown, itís just easier to get to.