First, period construction techniques require that skirt lengths be adjusted from the top of the skirt, not at the hem as in modern sewing. Finish the bottom edge of your skirt before you pleat or gauge it. It will be much easier to work with in this state, as well as being a more accurate construction method. If your skirt is to be worn over hoops it is better to make the back one to one and a half inches longer than in the front. When you are wearing it, it will appear to be level. If you don't it will very likely appear longer in the front than the back.
Second, if your skirt is unlined, attach a hem facing, from about three to six inches wide, to the bottom edge of your skirt. Use only about a half inch seam allowance, depending on how easily your material ravels. Turn the hem facing to the inside of the skirt. Turn it enough so the very bottom edge of the dress fabric is on the inside of the skirt. Sew the top of the hem facing to the skirt using small running stitches. Binding the edge of the skirt with hem braid is a fairly common finishing technique at the time, but it was not universal. It adds weight to the skirt as well as keeps the edge from damage and excess wear. Neatness doesn't really count here.
Third, by the war years, gauging had become a technique that was basically limited to garments such as children's dresses, cotton wash or "work" dresses and many times, sheer dresses. If you are making a good dress of silk or faux silk, good quality cotton, very fine wool, etc., the skirt would be more appropriately knife pleated, not gauged. Also, gauging doesn’t work well on bulky material.
Fourth, contrary to reenactor lore, skirts should be attached to bodices to create complete dresses, not a skirt and bodice combination hooked together. Depending on materials and basic style, a common way for this to be done was to make a skirt and bodice, then sew the two parts together or the skirt is simply gauged or pleated directly to the bottom edge of the bodice. On better dresses the skirt opening was just to the left of center front, now often referred to as a 'dog leg'. An extension is added to the waist of the skirt where it extends past the bodice opening. This extension is integral to dresses with visible waistbands. If a dress has an external waistband, a separate belt should be worn over it. Common cotton wash or 'work' dresses often had a center opening in the skirt.
(FYI, gauging is the 19th c. term for what is called cartridge pleating in modern terms)
Once you have seamed and hemmed your skirt, measure how long it should be. (One to four inches from the ground is about right.) Fold the excess length to the inside at the top of the skirt and crease. This turn over should be about one to two and a half inches long.
Thread your needle double length. The doubled over thread should be long enough to go around your waist, with at least a few inches extra. Wax your thread to strengthen it, make it glide more smoothly through the fabric and help keep it from tangling. Make a strong knot at the end of the doubled thread.
Sew one line of very even running stitches approximately a quarter inch from the top folded edge of your skirt. The amount of material you need to gauge down to fit the waist measurements will determine the length of your gauging stitches. I've found that stitches roughly one quarter inch long work well. The more skirt fabric and the smaller the waist, the longer you will need to make your stitches. (You might want to practice on a scrap of fabric and see what size stitches work best for you.) Stitch the entire length of the top of the skirt. Firmly tie off the end of your thread, leaving the stitches as loosely gathered as your thread allows.
Repeat the above steps, only sew the next row about one quarter to one half inch below the first row of stitches. Gauging is basically very organized gathering, so each stitch of this second row must line up exactly with each stitch of the first row for the gauging to work properly. This is why you want to keep your first row of stitches as loose as you can so you can spread the material flat above the second row where you are sewing. Even so, I know from experience it is easy to get out of alignment so watch your work very carefully.
Attaching Skirt to Bodice:
Once you have stitched both rows it is time to attach the skirt to your bodice or waistband, depending on the garment you are making.
First, divide the gauged edge of the skirt into a minimum of four equal sections, but preferably more. Match and pin each section division to the equivalently marked place on the bodice or waistband. Tighten both rows of gathering stitches to fit the waist, then tie off the gathering threads to secure the exact length.
Use the strongest thread you have to attach the skirt to the bodice. Use double length thread and wax it well. I also recommend using shorter lengths of thread for this purpose. Catch the top edge of the front of the first pleat and sew it just to the inside lower edge of the bodice or waistband. None of your stitches should show on the outside of your dress. Repeat this step at every pleat. I tend to take double stitches every few pleats to make sure the skirt is firmly attached. Watch your spacing closely to make sure the gauging is even. Gauging is time consuming since it must all be done by hand, but it is also a very forgiving technique.
Stroked Gathers, a variation
Stroked gathers were used for garments that needed a bit more strength than those that were gauged. Men's shirt sleeves, work aprons, petticoats, children's dresses, etc. were generally gathered using stroked gathers rather than gauging.
The main difference is, in stroked gathers the fabric is not folded at the top edge before the double row of stitches are put in. The other difference is, instead of the front point of each fold or pleat being stitched to the edge of the item it is being attached to, the top of the gathered material is enclosed inside the waistband of an apron, petticoat or child's dress or beween the shirt fabric and the shoulder facing at the top of a man's shirt sleeve and the two layers of the cuff at the wrist much the way modern gathered material is encased. The difference between period stroked gathers and modern is that the gathers are very neatly made and arranged. Period directions say to use the head of a pin to stroke the gathers into neat rows before sewing them into the waistband, etc. hence the term 'stroked gathers.'