A planning helper for the "ratio" and "block weights" you set when merging Stable Diffusion checkpoints. The actual merge happens in sd-webui-supermerger or the Merge Block Weighted extension — this tool just helps you decide the numbers. The first panel, Merge ratio, lets you pick a method — Weighted sum (A and B) or Add difference (A, B and C) — and drag the alpha (M) to see each model's effective contribution in the result. Weighted sum is result = A × (1−α) + B × α, so α=0.3 means 70% A and 30% B. Add difference is result = A + (B − C) × α, adding α times the B−C delta onto A (A is the base = 1, B is +α, C is −α). The formula is shown too, so you don't mix up which model dominates. The second panel, Block weights (MBW), builds the weight vector for merging the UNet block-by-block instead of with one flat ratio. Pick the architecture (SD1.5 = 25 blocks, SDXL = 19 blocks; base_alpha is separate), a shape (flat / ramp up GRAD_V / ramp down GRAD_A / smooth up / peak middle / peak ends) and the min/max weight, and it previews each block as a bar chart and generates a comma-separated weight string. Paste that string straight into supermerger's MBW weights field and set base_alpha separately. As a rule of thumb the shallow blocks (IN side) affect composition and large structure while the deep blocks (M / OUT side) affect texture and detail, which makes choosing a preset easier. Block counts follow the widely used convention, but they can differ slightly between extension versions, so confirm against what your extension expects. All math runs in your browser — the values you enter are never sent to any API or server.