# Hints on using individual LTSpice commands and the things the Help Manuals don't tell you about

.param

One of the more confusing aspects of using .param (at least when I began using LT) was where and when do you use the curly barckets {} ?

Beginning with the simplest definition, LT doesn't require curly brackets

.param res1 = 1000

This could be used to define a resistor of 1000 Ohms

However, in the real world, a parameter sometimes needs to be defined from other parameters.

To get results and not pull errors within LT, it becomes useful to use curly brackets. Without them - you can only nest (calculated) .param values, one parameter calculation deep.

Going any deeper (where one calculation depends on another etc) will invite LTspice to complain with an error.

**Correct Method { doesn't pull errors }**

- Comment line : Calculate capacitance
- -------------------------------------

.param length = {3e-2} .param width = {4e-3} .param area = {length * width} .param gap = {40e-6} .param Eo = {8.85e-12} .param Capa = { (Eo * gap) / area} .MEAS Capa_ PARAM Capa

The answer (from the error log ) is:
capa_: capa=2.95e-012

To see the results in LTspice
Use the Error Log (a better name would have been the results log)

**Incorrect method (pulls errors)**

.param length = 3e-2 .param width = 4e-3 .param area = length * width .param gap = 40e-6 .param Eo = 8.85e-12 .param Cap = (Eo * gap) / area} .MEAS Capa_ PARAM Capa

Error:
Warning Can't resolve .param cap=(eo * gap)area)

The quickest way to check a calculation before you commit it to a library
is to create a section of text within the LT schematic.
Set the text as LTspice directive (command) ,
then run the schematic

**Finding the measure results of a simulation**
Check your results in the error log
Found from the toolbar :
View/SPICE Error Log

**Suggestion:**
Set the Tools/Control panel/ Operation / Generate Expanded Listing
and tick (yes) to see a more comprehensive output listing - helps with debugging