Update: DFHack r3 comes with inventory monitoring screen built-in and includes an improved workshop UI written by ag. I recommend adding the following keybindings to your dfhack.init file:
keybinding add Ctrl-W@dwarfmode/QueryBuilding/Some "gui/workflow"
keybinding add Ctrl-I "gui/workflow status"
Pressing Ctrl-W with a job selected in a workshop will take you to the new
workflow settings screen. It's more complicated than the old screen. Arumba has created a
video tutorial that explains how to use it.
Pressing Ctrl-I or the Status option from the above screen will take you to the inventory monitor:
Note: the released version looks a little different to these screenshots as it's been re-written in Lua.This screen shows a list of all the item types being tracked by the plugin (known as "constraints"). The selection shows tracking of bars of coal. The green number on the right is my current stock level (81), the S means it's tracking stacks and 100 is the target limit. The colour of the stock level number indicates how "healthy" the stock level is based on current count and trend. Bright green is very good, green is good, red is bad, bright red is very bad. Specifically:
Stock > (limit - gap) : Bright green
(limit - gap) > Stock > (limit - gap*2) : Green
(limit - gap*2) > Stock > (gap*2) : Trending up = Green, Trending down = red, No trend = grey
(gap*2) > Stock > gap : Red
gap > Stock : Bright red
The limit number is also colour coded (as you can see some of them are red). Red means that there are currently no workshops producing that item (i.e. no jobs). If it's yellow, that means the production has been delayed, possibly due to lack of input materials.
The chart on the right is a plot of the last 14 days (28 half day plots) worth of stock history for the selected item. The bright green dashed line is the target limit (maximum) and the dark green line is that minus the gap (minimum). You can see the coal bars are slowly climbing upwards, but well below the minimum, hence the stock level is coloured green. Currently this stock history is not being persisted in the savegame along with the rest of the workflow data, so it will reset when you save and start again.
Along the bottom there are more controls. Note that they are now uppercase, so use "shift". Shift-O will toggle the sort order between alphabetical and severity. The latter mode puts the red entries that need attention at the top. You can see that in the following screen, showing how the drinks are trending down:
Since this list of constraints can be quite long, there is a "Search" option along the bottom. Search mode is always active.
Shift-A lets you add a new constraint directly without going through a workshop. This is useful to add tracking for items that cannot be produced (meaning you can't add a worksho job for it). For example, you can use it to track how many logs you have, complete with the history chart and colour coding based on your set limit/gap, so you can tell at a glance if the logs are depleting faster than they are being replaced. Or you can use it to track items you buy from merchants but can't produce yourself.
Further, you may want to read
this post (from the second paragraph on) about how to set specific input materials for workshop jobs, if you want them to link to specific constraints.