<$edit-text tiddler="weight" index="tmp" tag="input" type="number"/> <$button><$action-listops $tiddler="weight" $index="latest" $filter={{weight##tmp}}/><$action-listops $tiddler="weight" $index=<<now YYYY0MM0DD0hh0mm0ss>> $filter={{weight##tmp}}/>record</$button>
weight -> {{weight}}weight##latest -> {{weight##latest}}
try this snippet. It works for positive numbers but not for negatives ones.
<$edit-text tiddler="weight" index="tmp" tag="input" type="number"/> <$button><$action-listops $tiddler="weight" $index="latest" $filter={{weight##tmp}}/><$action-listops $tiddler="weight" $index=<<now YYYY0MM0DD0hh0mm0ss>> $filter={{weight##tmp}}/>record</$button>weight -> {{weight}}weight##latest -> {{weight##latest}}
<$edit-text tiddler="weight" index="tmp" tag="input" type="number"/>
<$button> record
<$action-setfield $tiddler="weight" $index="latest" $value={{weight##tmp}}/>
<$action-setfield $tiddler="weight" $index=<<now YYYY0MM0DD0hh0mm0ss>> $value={{weight##tmp}}/>
</$button>
\define makeAction(tiddler, number) <$action-listops $tiddler="$tiddler$" $index="latest" $filter="=$number$" /> <$action-listops $tiddler="$tiddler$" $index=<<now YYYY0MM0DD>> $filter="=$number$" />\end\define save(tiddler) <$macrocall $name="makeAction" tiddler="$tiddler$" number={{$tiddler$##tmp}} />\end
<$edit-text tiddler="weight" index="tmp" tag="input" type="number"/><$button><$action-listops $tiddler="weight" $index="latest" $filter={{weight##tmp}}/>
<<save weight>>
record</$button>
weight -> {{weight}}weight##latest -> {{weight##latest}}