1 Your mount
Start with the mount you own, then the counterweight shaft that's currently installed on it — every shaft is listed relative to the one your mount ships with, as Standard, Extended or Short. Add a shaft extension here too if yours has one attached. Together these set how far out along the shaft a counterweight can sit, which is what determines how much room you'll have to balance the load. Anything other than the standard shaft, and any extension, is added to the parts list in the results.
Shaft and RA axis details
2 Your telescope
Pick your configuration, then fill in each telescope — choose Other if it isn't an Astro-Physics model and type your own numbers instead. Each configuration's height field (rings + dovetail + saddle stack, crossbar, or top plate) opens with a typical value already filled in as a starting point; adjust it to match your own hardware. In single-OTA mode, if you've measured straight from the RA axis to the tube center yourself, check the box below and enter that distance directly instead.
FYI — counterweights only shift the balance point along the shaft, so they cannot correct a left-to-right imbalance across the crossbar. Slide the tubes along the bar for that.
Total instrument weight
3 Calculation settings
The safety margin sizes the recommendation for more than the telescope you entered, so you have headroom to add gear later. The rest is optional — by default the estimator prioritizes weights placed closer to the center of rotation. Separately, if you already own counterweights, enter how many of each below so the price reflects only what you still need to buy.