# Hints on using individual LTspice commands and things the Help Manual sometimes may not help you with

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## .Param and Curly Brackets

.param

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

Beginning with the simplest definition, LTspice 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 LTspice, 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 perhaps been *Results Log* or *Output 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:

Measurement "capa_" FAIL'ed

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