RPN : 1/3  RPN : 2/3  RPN : 3/3  start RPNenh  function repository 
2
+
3
=
gives 5.2
and then press sin
button. In this case you first enter the argument and then the function. this is less obvious..2
3
+
2
sin
+
and the sin
functions/operands are used after the values/arguments.your brains  manipulation on a RPN calculator 
Your brain, (normally) start spliting numerator (2+4)*(6+8) and denominator (57)  
You brain start (for example) with numerator, there are two expression : 2+4 and 6+8, it starts computing each of them 

It compute 2+4 it gives 6  2 4 + your stack display now 6, the result of 2+4 
and now it compute 6+8, it gives 14  6 8 + you stack display now 14 and 6, look how it keep all previous result. 
Now it multiply the result of the two previous operations 6*14 gives 84  * yes, we just need to press one key : * the stack now display only 84, the 6 and 14 have been consumed by multiply. 
Now (we keep 84 in mind)  it keeped on the stack, naturally. 
Let start with 57  5 7  it gives, 2 as expected. now on the stack, we have 84 and 2 
and finally we divide 84 by 2.  / that's it, you get 42 as result. 
Expression  on a classic calulator  on any RPN calculator 
1+2  1 + 2 = 4 keystrokes 
1 enter 2 + 4 keystrokes 
(1+2)/3  typing 1+2/3= is not safe, you have to use parethesis( 1 + 2 ) / 3 = 7 keystrokes 
1 enter 2 + 3 / 6 keystrokes 
you can see that in RPN, to enter serveral numbers, you have to use enter as separator :1 enter 2 enter 1 and 2 in the stack.
you can use the space key instead  
1+2+3+4  1 + 2 + 3 + 4 = 8 keystrokes 
1 enter
2 +
3 +
4 + 8 keystrokes 
sin(2)  2 SIN 2 keystrokes 
2 SIN 2 keystrokes 
sin(1+1)  SIN ( 1 + 1 ) 6 keystrokes (more and less, you may need to add = ,or maybe first parenthesis is already placed) 
1 enter 1 + SIN 4 keystrokes 
in RPN, argument(s) must always be placed before the operator, The following example demonstrates the difference between the RPN and nonRPN calculator.  
sqr( (3*4) ) and sqr( (3*4)+1 ) 
SQR ( 3 * 4 ) = : you have first result hereSQR ( ( 3 * 4 ) + 1 ) = 18 keystrokes 
3 enter 4 * DUP SQR : you have first result hereSWAP 1 + SQR 9 keystrokes 
It dupplicate intermediate result (3*4) for later use, to dupplicate something I introduce here the DUP command, to do a DUP, just press the enter key. we just continue our calculation, we compute SQR of 12... now on stack, we have : 12 and 3.46 (sqr(12)) Now, we want to use 12, we need to swap 12 and 3.46, to do that, lets introduce the SWAP command (in RPNEnh and MiniRPN, use the RIGHTArrow key) after the SWAP, the stack look like : we continue by adding 1 : 1 + , and performing the SQR of 13. now the stack looks like :
You have on your screen, the both results : sqr(3*4) and sqr ((3*4)+1). You can now do what you want with these numbers, to divide them, just press the / key.

enter
key is used to enter a number or to dupplicate it.1
2
3
enter
enter
1
enter
2
enter
swap
1
enter
2
enter
DROP