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var base=source1.substring(0,49);
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calcExposure();}

function calcExposure(){
var imgA=document.getElementById('aperture1');
var sourceA=imgA.src + "";
sourceA = sourceA.replace(/www./,"");
var valueA=parseInt(sourceA.substring(49,50));
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function writeBasics1(){
var str='';
str+='<div class="R-figure-desc202"><p class="figure-desc">';
str+='<a class="figure" href="javascript:void(0);" onmouseover="swapFigure(\'aperture_blur\',\'basics_aperture_wide.gif\');">Large<\/a> | ';
str+='<a class="figure" href="javascript:void(0);" onmouseover="swapFigure(\'aperture_blur\',\'basics_aperture_medium.gif\');">Medium<\/a> | ';
str+='<a class="figure" href="javascript:void(0);" onmouseover="swapFigure(\'aperture_blur\',\'basics_aperture_small.gif\');">Small<\/a>';
str+='<\/p><\/div>';
document.write(str);}

function writeBasics2(){
var str='';
str+='<div class="R-figure-desc217"><p class="figure-desc">';
str+='<a class="figure" href="javascript:void(0);" onmouseover="swapFigure(\'shutter_blur\',\'basics_shutter_slow.gif\');">Slow<\/a> | ';
str+='<a class="figure" href="javascript:void(0);" onmouseover="swapFigure(\'shutter_blur\',\'basics_shutter_medium.gif\');">Medium<\/a> | ';
str+='<a class="figure" href="javascript:void(0);" onmouseover="swapFigure(\'shutter_blur\',\'basics_shutter_fast.gif\');">Fast<\/a>';
str+='<\/p><\/div>';
document.write(str);}

function writeBasics4(){
var str='';
str+='<div class="R-figure-desc182"><p class="figure-desc">';
str+='<a class="figure" href="javascript:void(0);" onmouseover="swapFigure(\'light_meter\',\'basics_light_meter2m.gif\');">-2<\/a> | ';
str+='<a class="figure" href="javascript:void(0);" onmouseover="swapFigure(\'light_meter\',\'basics_light_meter1m.gif\');">-1<\/a> | ';
str+='<a class="figure" href="javascript:void(0);" onmouseover="swapFigure(\'light_meter\',\'basics_light_meter0.gif\');">0<\/a> | ';
str+='<a class="figure" href="javascript:void(0);" onmouseover="swapFigure(\'light_meter\',\'basics_light_meter1p.gif\');">+1<\/a> | ';
str+='<a class="figure" href="javascript:void(0);" onmouseover="swapFigure(\'light_meter\',\'basics_light_meter2p.gif\');">+2<\/a>';
str+='<\/p><\/div>';
document.write(str);}

function writeBasics5(){
var str='';
str+='<div class="basicsA1" title="Figure 6: Exposure Practice Tool">';
str+='<div class="basicsA2">';
str+='<img class="calc" alt="" title="" src="figures/basics_ec_top.gif" \/>';
str+='<div class="basicsA3">';
str+='<img class="calc_pointer" alt="" title="Larger Aperture"';
str+='onmouseover="this.src=\'figures/basics_ec_arrowup2.gif\'"';
str+='onmouseout="this.src=\'figures/basics_ec_arrowup.gif\'"';
str+='onclick="increment1(\'aperture1\',-1);" src="figures/basics_ec_arrowup.gif" \/>';
str+='<img class="calc_pointer" alt="" title="Smaller Aperture"';
str+='onmouseover="this.src=\'figures/basics_ec_arrowdown2.gif\'"';
str+='onmouseout="this.src=\'figures/basics_ec_arrowdown.gif\'"';
str+='onclick="increment1(\'aperture1\',1);" src="figures/basics_ec_arrowdown.gif" \/>';
str+='</div>';
str+='<img class="calc" alt="Aperture" id="aperture1" title="" src="figures/basics_ec_ap_3.gif" \/>';
str+='<img class="calc" alt="+" title="" src="figures/basics_ec_plus.gif" \/>';
str+='<div class="basicsA4">';
str+='<img class="calc_pointer" alt="" title="Faster Shutter Speed"';
str+='onmouseover="this.src=\'figures/basics_ec_arrowup2.gif\'"';
str+='onmouseout="this.src=\'figures/basics_ec_arrowup.gif\'"';
str+='onclick="increment1(\'shutter1\',-1);" src="figures/basics_ec_arrowup.gif" \/>';
str+='<img class="calc_pointer" alt="" title="Slower Shutter Speed"';
str+='onmouseover="this.src=\'figures/basics_ec_arrowdown2.gif\'"';
str+='onmouseout="this.src=\'figures/basics_ec_arrowdown.gif\'"';
str+='onclick="increment1(\'shutter1\',1);" src="figures/basics_ec_arrowdown.gif" \/>';
str+='</div>';
str+='<img class="calc" alt="Shutter" id="shutter1" title="" src="figures/basics_ec_sh_3.gif" \/>';
str+='<img class="calc" alt="=" title="" src="figures/basics_ec_equals.gif" \/>';
str+='<img class="calc_clear" alt="(tool not yet loaded)" title="" src="figures/basics_ec_bot.gif" \/>';
str+='</div>';
str+='<img class="calc" alt="Exposure" id="exposure1" title="" src="figures/basics_ec_pic_07.gif" \/>';
str+='</div>';
str+='<p>Try it yourself!&#160; Change the aperture and shutter speeds in the Exposure Practice Tool and see the difference in the exposure.&#160; Change one, then think about how to adjust the other to bring the exposure back to where you started.&#160; Notice how the same exposure can be created by many shutter speed and aperture combinations.';
str+='<br />';
str+='<br />';
str+='</p>';
document.write(str);}

function writeBasics6(){
var str='';
str+='<div class="R-figure-desc202"><p class="figure-desc">';
str+='<a class="figure" href="javascript:void(0);" onmouseover="swapFigure(\'focus_blur\',\'basics_focus_pic_n.gif\');">Near<\/a> | ';
str+='<a class="figure" href="javascript:void(0);" onmouseover="swapFigure(\'focus_blur\',\'basics_focus_pic_m.gif\');">Middle<\/a> | ';
str+='<a class="figure" href="javascript:void(0);" onmouseover="swapFigure(\'focus_blur\',\'basics_focus_pic_f.gif\');">Far<\/a>';
str+='<\/p><\/div>';
document.write(str);}